How to quickly charge your smartphone: fast charging technologies in detail

4/22/2025 at 11:57:44 PM

I feel something is missing at the moment with our ability to choose on the device how I want it to charge. Would be nice to plug the phone in and unless I say otherwise it does a nice slow charge even if the cable and charger is capable of more. But if I press a button on the front after I plug it in then I can select fast and it goes as quickly as the combination allows. Its irritating to have to have different chargers for this to preserve the battery.

Its pretty bad that only recent phones have started to add the ability to charge to only 80% to keep the battery in the optimal zone to extend the life given how long we have known that 80% was the optimal maximum. There are also a few phones now able to power themselves from USB without using the battery which if you leave them in chargers a lot throughout the day and night seems like a good feature to have to preserve the battery further.

Maybe all the complexity around this is too much and people just want to plug it in and quick 100% as quick as possible and will change their phone regularly but its pretty wasteful. We ended up going through lots of special chargers that all do very similar things and now you get a device and it often doesn't even come with a cable let alone a charger and you are digging through the specs of your charger, cable and device to work out if its all going to mesh correctly together or you'll be stuck on slow mode. We have ended up with so many standards for getting quicker than the basic charge its going to take a while for all these devices to age out and in the meantime chargers are going to be doing QC and PD and a host of other things besides for a while.

by PaulKeeble

4/23/2025 at 12:28:00 AM

> Maybe all the complexity around this is too much and people just want to plug it in and quick 100% as quick as possible and will change their phone regularly

It's this, 100%. The nerds that care about charge temperature and battery degradation and proliferation of incompatible charging standards are a rounding error, most people just want to know it can charge fast in case they forget and need to leave soon.

I am happy with my Chargie [1], an interposing dongle which provides a Bluetooth receiver and app that lets you set arbitrary preferences on your phone and fast charge, slow charge, or turn off the charger at configurable state of charge setpoints or times.

[1] https://chargie.org/product/chargie-c-basic/

by LeifCarrotson

4/23/2025 at 1:40:01 AM

I had never thought such thing existed commercially. Mainly because I had looked for it myself in addition to asking about it without results.

It needs an app but doesn't mention interoperability. There, I said it. It is not perfect.

At least they allow you to set-up-in-app-and-use-without-app which is more than many products.

by catlikesshrimp

4/23/2025 at 1:51:57 PM

There is a built-in charge limiting feature in Android now, so that doesn't need any apps, but the only options are limit to 80% or 100%. But for something like this, how else are you going to get your phone to tell a charger when to turn off? Apparently, making an API that allows devs to reliably stop charging in software is too risky, so IoT devices with companion apps are the solution, of course. Not to mention the device manufacturers are probably quite happy to have batteries degrade significantly after warranty ends.

by hnuser123456

4/23/2025 at 2:13:45 PM

>needs an app

Now imagine the same product but with different physical toggles or buttons on it for all the different charging modes. No apps. That'd be great.

by Funes-

4/23/2025 at 8:40:04 PM

Switching between 500 mA, 2.1A, and USB-PD or QC is technically simple, but again you're making consumer electronics for a very, very small group of people.

How would it determine when the attached device reaches 80% state of charge? Or what the time of day is? How could you program a schedule for weekdays and weekends?

There are good reasons for Chargie to have an app, it's not just there to siphon up analytics.

by LeifCarrotson

4/24/2025 at 6:35:56 AM

> How would it determine when the attached device reaches 80% state of charge?

The same way it determines that the battery is fully charged. It is a solved problem.

by hulitu

4/24/2025 at 7:49:47 AM

This information is not available on the USB-C connection. The 'charger' is simply a power supply, it does not actually manage the regulation of current into the battery.

by rcxdude

4/24/2025 at 1:13:28 AM

I'm thinking something like a switch on the side to switch between slow, fast, and using the app.

by timando

4/23/2025 at 2:29:18 PM

Or even a way to communicate this to the charger from the phone using the vendor extension to PD protocol negotiations…

by baby_souffle

4/23/2025 at 4:30:05 AM

Feel like all of this would be a bit irrelevant if we just had easily replaceable batteries. Phone batteries don’t cost that much.

Rather than worrying about charge speeds and charge %, I’d rather just slap a new battery in after 4 years.

by Gigachad

4/23/2025 at 3:50:05 PM

In a world where I can have my iPhone battery replaced for $99 by Apple with official parts and a quick turnaround, my desire for self-replaceable batteries is completely gone.

I’ll take the reduced size, lower weight, sturdier construction, and better waterproofing I get from the current build style.

Saving tens of dollars and an hour or two of my time every 4 years isn’t worth the compromise.

by Aurornis

4/23/2025 at 4:53:15 PM

Instead you could spend $10-20, be able to buy a couple in case you wanted some backups in certain situations and not have most people replace their phone when their batteries start losing juice and make their system feel sluggish.

All to have a slight thinner device.

by xandrius

4/23/2025 at 8:23:50 PM

Yeah, I miss the old Nokia battery system and ironically technology has made it all more painful since it is now once or twice per day instead of per ~week that you might realize you want to go out but have put off charging.

by satanfirst

4/23/2025 at 5:51:20 AM

Totally agree. Tbh I never needed the phones to become as thin as cardboard. At the cost of sacraficing the ability to easily remove/replace the battery I certainly never wanted it.

by sans_souse

4/23/2025 at 12:18:23 PM

>I never needed the phones to become as thin as cardboard

And it is only thin until you put on the bulky case. If phones put a real battery and intigrated basic protection, it would still be thinner than the current small battery/outer case situation. Most people don't need tank-like Otterbox protection, they just need something that keeps bumps and small drops from shattering something.

by 542354234235

4/23/2025 at 4:57:27 PM

A long time ago, I had a phone with replaceable battery. I would much rather charge phone. I had to change the battery every few hours, partly because the battery was small to make replaceable and partly cause wireless sucked.

Battery life is much better now. I put phone on wireless charging pad and it is always charged when I need it. I use it all day and still have power. I carry power banks in bags if need it. External battery is better because it works with any device without having device specific batteries. Also, there are now batteries that magnetically attach to phone and wirelessly charge.

It would be nice if it was easier to replace battery, but don't need replaceable battery every day for something that happens in couple years.

by ianburrell

4/23/2025 at 5:07:41 PM

The battery in your current phone is not that much bigger than the replaceable cells of yore.

The big difference is simply that battery chemistry has improved and new cells have more energy per volume.

There is no technical reason at all that we can't have replaceable cells with the capacity of current internal batteries. Unless you count waterproofing, which I've always viewed as nothing more than an excuse for planned obsolescence. There are definitely ways they could engineer water-resistant phones with replaceable cells.

by mystified5016

4/23/2025 at 3:46:16 PM

give me a battery door and a charging cradle so I can have two batteries, one that charges on the cradle and one in the phone to use and I'll swap them whenever I need, and never have to wait.

The same way my Game Boy worked in the nineties with NiMH batteries. Why did we abandon that pattern?

by dingnuts

4/23/2025 at 4:41:15 PM

Replaceable batteries require thick case and also it's not easy to make the case waterproof. Consumers prefer thin waterproof cases.

by vbezhenar

4/23/2025 at 9:06:32 PM

I think most people prefer an older phone style. The difficulty is that the screen implies a large surface which then requires thinness to not have a problem of large volume as well as general awkwardness.

by satanfirst

4/24/2025 at 6:37:56 AM

> Feel like all of this would be a bit irrelevant if we just had easily replaceable batteries.

"Don't you want to be online all the time, so we can spy on you ?" . Sincerely, FAANG /s

by hulitu

4/23/2025 at 2:16:53 AM

Adaptive Charging on Pixel devices gets most of the way there: it will learn how long it's typically on the charger each day, and automatically slow the rate of charge to match, so that it finishes approximately an hour before you usually unplug it.

There's a manual option to turn it off (charge at full rate this time only), but not to manually turn it on (such as giving it a target time to be fully charged). Older Pixels used what time the alarm was set as the target time to finish charging, which I preferred as someone who doesn't wake up at the same time every day; I'm not sure why they took that away.

by dpifke

4/24/2025 at 8:33:08 AM

The adaptive charging used to be great for me, and then I had a baby. Now I get up a few times in the night, and so the adaptive charging just defaults to full rate. My night is still going to "end" at the same time so slow charging is fine, but my phone doesn't know that. I wish I had an override.

(I do have an old, lower wattage charger beside my bed to limit the charge rate)

by rkangel

4/23/2025 at 7:30:19 AM

Another problem is the constant charging and discharging of battery while connected to external power. I believe the latest pixels got or will soon get the ability to run directly off the wall when connected to certain chargers.

I would love to see this technology come to all phones. 80% cap might be controversial but I don't think what I am asking for is controversial in the least.

by mcny

4/23/2025 at 9:00:21 AM

> Another problem is the constant charging and discharging of battery while connected to external power.

Is that actually the case? Anecdotally, all my devices which spend 99% of their time connected to external power show the least degradation in reported capacity and the best preservation of their original battery life. I'm talking about iPhones, macbooks and hp laptops.

For the latter, I have two basically identical ones, one for work and the other for home (same model number, same generation, same battery p/n). The home one rarely if ever runs on battery, it has something like 50 cycles in 4 years. The battery lasts pretty much as when it was new. The other runs often on battery and it only lasts half as much. I doubt it's a lemon, because it's the standard issue laptop at work, and my colleagues' are in the same boat.

My iphone 14 pro's reported battery health has also degraded much faster than my iphone 7's. I use it much more often on battery than the old one which spent 90% of its time plugged in. But since the devices are different, the comparison isn't as meaningful as with the laptops.

by vladvasiliu

4/23/2025 at 4:00:29 PM

Some devices will notice when they've been plugged in for a very long time, and will automatically discharge the battery to 80% or so, but continue to report 100% state of charge to the user.

Chemically speaking, Li batteries do degrade much faster when kept at 100% for weeks on end compared to being stored at 50%, but not as fast as cycling it. The absolute worst case (without cycling) is being stored at 100% at warmer temperatures, like 40C. They will lose over 10% within a month in those conditions. I highly suggest a laptop cooler for any desk where you may use a laptop plugged in for extended periods.

by hnuser123456

4/23/2025 at 7:41:50 PM

That's... really not how this works. As a person designing lithium management circuits, you typically have a very small delta-V for top-off charging. We're talking ~0.1V. Once full, the charge circuit disconnects. If the battery is under load or self-discharges below your dV, charging starts back up usually at a very low current. Top-off is also totally optional, it's just a common feature.

Additionally, only the cheapest of cheap garbage phones would behave the way you imply. Charge controllers are readily available from TI et al with battery bypass. When the battery is full, the system runs on external power exclusively, except for the top-off charge.

It's really a pretty standard feature. You can get controllers with and without this, but you'd have to be either extremely cheap or extremely dumb to not use a controller with battery bypass in an application like a phone.

Based on my own testing, my pixel 8 will run on USB. No current fluctuations that would indicate battery cycling, just a constant draw. My previous Samsung also behaves this way.

You're right that cycling the battery this way is bad for them, that's why competent engineers don't.

by mystified5016

4/24/2025 at 4:46:58 AM

I found this source about pixel phones and bypass charging. I also know anecdotally that leaving phones plugged in with screen on, I have gotten spicy pillows more than once. I would love to learn how to avoid this spicy pillow problem.

https://old.reddit.com/r/GooglePixel/comments/1ha8tv9/pixel_...

by mcny

4/23/2025 at 3:19:20 AM

It is absolutely too much work. It's incredibly easy to get bogged into the weeds of config stuff like this and almost no one will care. if they did, I bet it's turn into a cluster of hearsay about magic settings that make almost no practical difference.

Also, I'd argue it's not obvious that 80% charging is better for most people. You're taking an immediate 20% cut to battery life, and chances are it will take years for it to actually be better than charging to 100%. I guess it's good to have the option, but only if you almost never need that last bit of capacity.

by Panzer04

4/23/2025 at 3:30:03 AM

I don't like the 80% option because every time I'm leaving the house for extended periods, going hiking or traveling I think "is it worth it to go through 3 settings screens to take an extra 15% charge with me?" 15% is a micro optimization and it was easier when there was no option and I never thought about it. I want to think about other things, not my phone's battery capacity.

by shpx

4/23/2025 at 4:21:26 AM

Yeah but in android or something this would be just another "quick settings tile" like the "flashlight" or "night light" or "battery saving mode". You could call it "overcharge mode" or "extra battery mode", and like the "night light" mode it would get disabled once you reach a full charge, so you don't have to dig into settings to turn it off again.

by beeflet

4/23/2025 at 8:52:36 AM

I think that's the case on my mom's Android. And it's a basic Samsung galaxy something-or-other, nothing customized.

by vladvasiliu

4/23/2025 at 1:36:49 AM

My Galaxy S21 lets me pick between normal, fast, or super-fast charging in the settings. Not quite one tap, but it does let you do it.

That said "super-fast" charging on it is like 18W and still about an hour from 20%, so it doesn't really qualify as fast charging IMO, and at an hour is certainly not going to be causing any excess battery wear. It's just normal speed.

by Saris

4/23/2025 at 1:49:45 AM

https://en.m.wikipedia.org/wiki/Quick_Charge

Quick charge started at 7.5W

My charge "Standard" was set in the time 500mA was supplied by most phone chargers. Just saying I am old.

by catlikesshrimp

4/23/2025 at 1:57:45 AM

For sure, but for terms of battery wear all that really matters is the time to charge. Under 1 hour is getting into the realm of 'really fast' and heat inside the cell starts to become an issue.

by Saris

4/23/2025 at 3:44:08 AM

Charge it up to 80% in the firmware but show 100% in the UI. Wear leveling algorithms probably do something similar already.

by jallmann

4/23/2025 at 9:11:45 AM

100% is always just an arbitrary value chosen by the device or battery manufacturer, there's no 100% level inherent to a battery. Unfortunately there's very few manufacturers that will tell you their estimated number of cycles and none (as far as I know) that will give you the number of cycles as a function of charge percentage.

by LiamPowell

4/23/2025 at 7:54:52 PM

Yes, but no. There is an absolute number that the circuitry tracks internally. The hardware does several kinds of measurements to count every joule entering or leaving the battery. The system knows exactly how much energy is in the cells.

The arbitrary value is what voltage you stop charging at. You set your maximum cell voltage and stop charging once you reach that voltage AND input current is below a threshold. Once charging is complete, you store the current energy value as the latest full capacity. That value then becomes the 100% mark.

Remember that batteries lose capacity over time. You must continually scale your state of charge percentage to the actual state of the battery.

The final charge voltage is a tradeoff between safety, longevity, and usable capacity. Higher voltages squeeze a few more joules into the cell at the cost of much faster degradation and increased risk of catastrophic failure.

A cycle count figure on lithium cells is pretty much worthless. It depends quite a lot on exactly how you cycle the battery. A 100 to 0% cycle is much, much more damaging that a 100-50% cycle. Higher currents and temperatures degrade the cell faster. Most cell manufacturers I've seen do give cycle counts under specific test conditions, but that's hardly applicable to real use cases.

by mystified5016

4/23/2025 at 10:11:45 AM

It's not arbitrary. Lithium batteries charging uses voltage termination, and the usual cutoff for 100% on lithium-cobalt batteries (so not LiFePO which is not yet widely used on phones) is 4.2 volts. It's the same for all batteries I've ever used or heard about. You can charge it to higher voltages, but basically nobody sane does that as it quickly becomes dangerous, and 4.2 is pretty much the standard voltage.

by homebrewer

4/23/2025 at 10:34:15 AM

Pouch batteries straight from distributors might all recommend 4.2V, but what's actually used in phones varies a lot. The Samsung Galaxy S21 for example charges all the way to 4.4V. I don't have a huge sample size to work with, but I have seen a number of recent Samsung batteries degrade alarmingly fast, likely because of this.

According to [1], the S24 has gone all the way up to 4.45V.

[1]: https://old.reddit.com/r/techsupport/comments/1ayqveg/samsun...

by LiamPowell

4/23/2025 at 4:03:19 PM

I was surprised to read the label on a GoPro battery and see it rated to 4.4v or thereabouts.

I used to build quadcopters around 2015, and some of the battery mfgs released "LiHV" batteries, which were supposed to be safe up to 4.35v, however if you actually charged them that high, they would puff up like balloons after only a couple flights. Maybe with the cumulative advancements in the last 10 years, they've been able to push up the max voltage more safely.

by hnuser123456

4/23/2025 at 5:51:52 PM

LiHV has nearly taken over, especially in racing and 1-2S powered micros.

by creaturemachine

4/24/2025 at 7:55:14 AM

There's been a slow creep in voltage as the manufacturers chase ever higher energy density.

by rcxdude

4/23/2025 at 7:37:34 AM

Don’t forget a “defeat” mode where the system detects you’re a reviewer and really truly does charge to 100%.

by Scoundreller

4/23/2025 at 1:04:09 PM

will change their phone regularly

Yeah, I need my phone to just last until the end of the day. The charger is on the night stand. To Android's credit, if I have an alarm set, it'll time the charge to reach 100% as the alarm goes off.

With these habits, I've never had to replace my phone due to the battery, so going the extra mile to preserve the battery seems like an exercise in futility...

by dfxm12

4/23/2025 at 5:04:19 PM

Google and Samsung phones have options to disable fast charging, though it's hidden in the system menus. Google phones have a feature that 'intelligently' (linear regression) scale down charge current at night so it reaches full just before your set morning time.

The Samsung phone I had was pretty good, you had separate options to disable fast charging on either wired or wireless.

But really my solution is quite simple: none of my habitual charging spots have a fast charger, they're all 5V 2A adapters. I do have a couple of fast chargers around the house, I just don't use them unless I really need to. It's a deliberate decision to fast charge.

That and where applicable I limit my devices to 80-90% full charge. My Linux thinkpad has firmware level support for this, it's very nice.

by mystified5016

4/23/2025 at 11:58:40 AM

I use ACCA[0] to select my charge rate and limit. This can also set battery idle mode (power from USB without using the battery) when the charge limit is reached if the hardware supports it. I usually limit it to 60%, and charge at 500mA when I'm not in a hurry.

Maybe that's too much fuss for most people, but I'm still using a five year old Pixel 4A on the original battery and its showing no signs of reduced battery performance. I probably wouldn't put in the effort if it was easy to replace the battery, but it is not. I might be a little less aggressive about it if I liked any current phones, but I do not.

[0] https://f-droid.org/packages/mattecarra.accapp/

by Zak

4/23/2025 at 6:40:12 PM

Samsung should at least make a quick settings toggle for fast charging. I constantly have to dig into that menu which is hidden deep down in settings.

There's one for battery protection (the 80% thing) but not for fast charging.

by wkat4242

4/23/2025 at 3:53:47 PM

I actually built this for myself on my previous phone using Tasker. If you have root you can just set the charge voltage (basically redefining 100% as 4.1V or something to limit charge %) and current to whatever you want. It was especially nice to be able to limit the current to like 500mA while using Android Auto because GPS and data use gets the phone hot enough already. That phone's barely aged in the two years or so I had it.

On my current phone I use wireless charging overnight and the 80% limit and I think that gets me most of the benefits of that hacky solution without requiring root.

by monkemonke

4/23/2025 at 5:52:15 AM

My hack is to only use fast charging bricks, but at home I charge my phone wirelessly. So that means in practice I rarely fast charge it.

Yes, it does heat up due to energy losses, but I suspect that's way less hard on the battery than the same amount of heat from actual high current charging (please correct me if I'm wrong).

This means the only drawback is that my phone charging is cost-inefficient.

by rconti

4/23/2025 at 7:33:12 AM

There has been some noise about wireless charging causing faster battery degradation because the batteries are usually warmer with wireless charging. Could be a specific hardware or firmware defect only on the iPhone 14 line, I am not sure.

by mcny

4/23/2025 at 4:08:53 PM

There are some wireless chargers with builtin fans. At least the pixel stand gen2 does.

by hnuser123456

4/23/2025 at 4:06:35 AM

Most multichargers solve it by having faster and slower charging ports. This may be not an app, but a nice / simple hardware based solution

by xiphias2

4/23/2025 at 1:03:23 PM

PD was never deployed for USB-A and was removed from the most recent standard. The grandfathered nonstandard charging protocols will linger around so long as type-A ports are the default.

by kevin_thibedeau

4/24/2025 at 6:33:49 AM

> Would be nice to plug the phone in and unless I say otherwise it does a nice slow charge even if the cable and charger is capable of more. But if I press a button on the front after I plug it in then I can select fast and it goes as quickly as the combination allows

This is Windows 95 style UI. We don't do that anymore. We are "smart" now. With blockchain security. And you can choose any colour you like, as long as it is a shade of grey. /s

by hulitu

4/22/2025 at 11:15:40 PM

>In such a situation, the best solution is slow charging, for which a low-power charger from your old feature phone is ideal.

It seems like most Android phones now have a feature that does this, though you have to enable it. Mine asked me to put in the time I go to bed and the time I wake up, and it slowly charges the battery over that time period to 100%

by robotnikman

4/22/2025 at 11:51:00 PM

My Pixel just bases this off of the morning alarm clock. Since I don't like waking to an alarm, this just means that I have a permanent silent 9am alarm.

I do hope that USB PD and (to a lesser extent) Qi takeover the charging space. There is really no reason to have every SoC vendor create their own incompatible fast charging standard.

by avidiax

4/22/2025 at 11:33:51 PM

I never even strictly enabled it, but I'm a big fan. My pixel 5 from 2020 still easily gets a full day of battery life, and without direct evidence, I suspect always slow-charging has helped with that.

by yathern

4/23/2025 at 5:11:59 AM

> the best solution is slow charging, for which a low-power charger from your old feature phone is ideal. These devices offer a small power output of 2–5 W, stretching the charging process to 5–7 hours depending on the adapter's power and the battery capacity. This way, your phone's battery charges under the best conditions, minimizing degradation

I've been charging my iPhone this way since the iPhone 4 (trickle charging overnight) and have noticed zero improvement in battery degradation performance vs. fast charging.

As a current example, my iPhone 15 Pro, purchased a month after launch, is at 85% capacity.

by mvkel

4/23/2025 at 12:35:35 PM

Anecdotally speaking, the 80% limit seems to be key to better battery aging long term.Anecdotally speaking, the 80% limit seems to be key to better battery aging long-term.

My launch-day iPhone 15 Pro Max is at 95% battery health. That phone has had the 80% limit enabled since day one, and I very rarely have had to increase it for specific busy days.

My previous iPhone 12 Pro Max very quickly descended to 88% battery health after a year.

My charging habits remain the same: fast and furious Magsafe/Qi/Qi2 charging every time there is a charger nearby (remote worker, so that’s almost all the time).

I do have unpleasant thoughts about the 80% battery charge limit not being available on anything older than the 15, since it turns out it can be sideloaded via Nugget and MobileGestalt manipulation.

Not enough to push me away from the walled garden (these phones are aging better than my previous flagships from other ecosystems), but a reminder of the rough edges in it.

by icebergonfire

4/23/2025 at 10:02:18 PM

It seems strange, though, that one would habitually charge to their "effective" capacity of 80% for the purpose of preserving the battery for the next owner

by mvkel

4/23/2025 at 11:34:48 PM

I do it for the purpose of preserving the battery for myself down the line. I'll go for a full charge if I expect to need it, but 80% is usually more than enough so why put unnecessary wear on the battery?

by calfuris

4/24/2025 at 5:49:46 AM

isn't that intentionally creating a lot of mental anguish every day (trying to make 80% last the full day) in exchange for just one day of simplicity at some theoretical point in the future?

Feels a bit like worrying about tomorrow stealing joy from today

by mvkel

4/24/2025 at 2:28:47 PM

> isn't that intentionally creating a lot of mental anguish every day (trying to make 80% last the full day)

Not at all, I only use around 40% per day.

> in exchange for just one day of simplicity

More like avoiding months of that mental anguish in the future because my phone can still easily handle the 40% I use instead of having degraded down to where that is the limit.

by Izkata

4/24/2025 at 10:39:38 AM

Homo sapiens is a genus full of anxiety, as our ancestors who didn't "worry about tomorrow" either died from hunger, or got killed by those who did. Anxiety is an evolutionary feature.

by maratc

4/25/2025 at 2:59:15 PM

> Anxiety is an evolutionary feature

I used to think this way. Spent decades justifying it as a motivator. It's a trap.

It made sense if you were risking your life whenever you went to get food. If you're trying to recreate those feelings by undercharging the battery of your smartphone, you're just bored

by mvkel

4/25/2025 at 10:12:26 PM

It doesn’t matter. You’re not trying to recreate anything. Your brain is just wired that way already. You’ve got it from your parents, who got it from their parents, all the way to our predecessors in Africa.

by maratc

4/23/2025 at 7:25:10 AM

My iPhone 15 Pro Max, first use on September 2023 is at 98% capacity. Charged mostly on a wireless charger and the charge limit set to 80%.

by SietrixDev

4/23/2025 at 10:03:15 PM

If you're capping the charge to 80% always, the only beneficiary of the total capacity of the battery is the next owner. Like wrapping your furniture in plastic.

by mvkel

4/23/2025 at 10:41:59 AM

Iphone 15 Pro here, first use Nov 2023, is at 94% capacity. Mostly wireless charging at 80% too. 290 cycles.

by LUmBULtERA

4/23/2025 at 12:48:41 AM

Many phones/chargers with propietary protocols are also equipped with USB PD compatibility. For example, you can pick up some random Xiaomi phone labelled at 90W and expect it to charge at more than 20W with USB PD, or even ~90W on some vivo models.

I don't see why the best charger is the old feature phone's charger - the point in fast charging is that you don't have to wait too long if in a hurry. That charger is the "best" if only you have almost unlimited time to charge, like during the night.

by cyp0633

4/23/2025 at 1:22:15 AM

One thing I was hoping the article would explain is how fast charging actually works: IE, how does the charge controller turn incoming electricity into a full battery?

The reason why I switched to wireless charging was because I had a phone go bad due to problems with the charge port. USB-c ports on my Pixels to tend to clog with dust and other debris, but as long as I use a wireless charger, it doesn't matter.

by gwbas1c

4/24/2025 at 2:32:03 AM

It boils down to applying a carefully controlled charging voltage (higher than the current battery voltage) to the battery. I would assume that the voltage is adjusted to achieve a specific charging current.

With PPS (programmable power supply), AFAIK the phone will typically ask the charger for a voltage twice as high as it wants to send to the battery, possibly a bit more to compensate for losses in the cable, then halve that with a highly efficient charge pump (https://en.wikipedia.org/wiki/Charge_pump).

The best (most "gentle") way of charging a battery would likely be a phone that is intentionally not trying to fast charge, connected to a PPS-capable power supply. This would minimize losses and thus heat within the phone without charging the battery faster than necessary. I suspect that the difference to charging off a non-PPS charger is negligible in practice.

Wireless charging creates a lot of waste heat, which isn't great for the battery.

by tgsovlerkhgsel

4/23/2025 at 1:48:29 AM

All charging does is reverse the flow of lithium ions through the electrolyte that happens when the battery discharges.

Wireless charging is usually worse long term because of the extra heat the coils create from the waste energy. It's probably about as bad as the really fast charging phones do now though. I principally have mine do a slow charge over night these days though as is mostly last through the day.

by rtkwe

4/23/2025 at 1:38:59 AM

It's basically as simple as a buck converter that reduces the incoming voltage.

Phone batteries need either 4.2V or 4.35V to charge fully, so whatever voltage comes in (5-20V typically) at whatever current, gets reduced down to the correct voltage and current to charge the battery.

by Saris

4/22/2025 at 10:51:28 PM

I don't think Apple was the first to use the magnets to align the phone to the charger. I think I had a nexus 5 that had the magnets in the phone and google Qi charger -- that would perfectly align the phone and charger.

by billfor

4/23/2025 at 5:33:37 AM

Pretty sure magnet alignment was part of wireless charging with the Palm Pre, and I'm not even a Palm person (I did have an IBM branded Palm Pilot, but it was very outdated when I got it for almost no money, and it didn't call to me)

by toast0

4/23/2025 at 1:41:28 PM

I realize that planning is hard for people, but the most important thing is to budget the battery so you are between 30 and 80 percent daily. Get an app that will alert as low battery at 30% and stop charge at 80%. Spend some money and put charging spots wherever you need them. Doing this will easily double a lithium ion battery lifetime.

https://batteryuniversity.com/article/bu-808-how-to-prolong-...

by 1970-01-01

4/23/2025 at 1:56:48 PM

With modern smartphones, with the right options, that's going to be rather typical.

There is usually some setting to limit charging to 80%, and while it depends on your model and usage, going down from 80% to 30% at the end of the day is quite typical. Then you can charge overnight (preferably using slow charging) back to 80%.

But when you need it (ex: travel), you have the option to unlock full charge and use fast charging.

by GuB-42

4/24/2025 at 5:47:19 PM

> Xiaomi HyperCharge requires an original Xiaomi cable and charger because the USB-A connector used includes an additional physical contact—five pins instead of the usual four.

This is a regular superspeed USB-A connector (albeit with both SSTX/SSRX contact pairs omited). Standard SS USB-A cable would work just fine here:

https://en.wikipedia.org/wiki/Usb3#Connectors

by kees99

4/23/2025 at 1:22:47 AM

In China, replacing an Android smartphone battery is relatively inexpensive—around 100 RMB (approximately 15 USD) for a full battery replacement service. Therefore, we treat it as a consumable item and don't worry much about battery wear. Fast charging and reaching 100% charge are what matter most, as battery concerns shouldn't interfere with my other priorities.

by Mike-14

4/23/2025 at 10:31:39 AM

On a rooted phone you can install acc which lets you set a maximum percentage to charge to, percentage at which the phone shuts down, max charging current and voltage, max charging temperature, etc.

by eulgro

4/24/2025 at 6:55:16 AM

A lithium-ion battery cell for a smartphone costs the device OEM somewhere between $2 to $4 ($0.10/Wh is todays rate?).

Are we seriously discussing how fast charging can lead to 1.6% degradation of 2-4$ every 100 days? Maybe it's better to discuss why to replace it at the service center costs 50$

by gloosx

4/23/2025 at 12:18:32 AM

It is annoying that while the connector itself is now finally standardized, the details of implementation diverge. So while you may be able to charge, it'll be slow charge.

by sega_sai

4/23/2025 at 7:38:33 AM

This was my complaint when the connector was standardised. There’s also no guarantee that the USB c cable you buy will support it even if your phone and plug do.

by maccard

4/23/2025 at 10:13:35 PM

Off topic question - this quick charging question only become largely relevant since we no longer have removable battery's. My question is how much space is saved by having non removable batteries. ( I remember that's the excuse when non removable batteries first cam out )

by asdefghyk

4/23/2025 at 2:35:02 PM

I have a bunch of Apple stuff, and I've learned to take the AirPods cases off of the MagSafe charger, as soon as they have reached 100%.

If I leave them on, they get warm, and the pods (not necessarily the case) lose their charge.

by ChrisMarshallNY

4/23/2025 at 2:08:30 PM

I have so many different chargers, brands, cables, and adapters and honestly have never checked what any are capable of.

I’d like to just buy 10 of a given charger, maybe with a couple of adapters for different devices.

What’s the best option today?

by rpicard

4/24/2025 at 2:38:27 AM

If you're buying modern phones and expect the charger to also be used with your future phone, I'd look for a USB PD capable power supply with PPS support. (Edit: Many of the phone makers that are listed as having proprietary technologies support PD on newer phones. Since the EU mandates USB PD, I would expect the vast majority of new devices to support it at least well enough that you won't need anything else.)

Rather than 10 of a given charger, consider a smaller number of GaN chargers with multiple ports, but be aware that many of the "smart" ones will reset all ports if any port is reconnected or renegotiates. I have a "smart" charger capable of outputting 100 W on one port or some mix of wattages on multiple ports (mainly for travel), and a "dumb" multi-port charger that I use both for slow charging of phones and for powering IoT devices that I don't want to be reset. The latter simply has multiple USB-A ports, which lets me charge almost anything - either with an A-to-C cable, or A-to-whatever-that-device-needs (either Micro-USB, Mini-USB, or something proprietary).

by tgsovlerkhgsel

4/24/2025 at 2:47:02 AM

Good advice thank you. Makes me think maybe a slow charging set up by the bed and a fast charger down in the living room / kitchen / for travel.

Then maybe another slow charger for all those miscellaneous things around the house.

by rpicard

4/23/2025 at 3:29:37 PM

> What’s the best option today?

This article has all the info you need to be able to answer that question. But the answer is, it depends what phone brands you use.

by esperent

4/23/2025 at 7:55:46 AM

Unfortunately I’m not sure this article is good, as it doesn’t seem technically sound.

Disclaimer, I was expecting an article with such a title to talk more about silicon anode batteries, or perhaps LTO (lithium titanate oxide) batteries that can charge in about 6 minutes (10C). It’s fine that the article doesn’t talk about that… however some of its other claims are a bit problematic.

> In such a situation, the best solution is slow charging, for which a low-power charger from your old feature phone is ideal. These devices offer a small power output of 2–5 W, stretching the charging process to 5–7 hours depending on the adapter's power and the battery capacity. This way, your phone's battery charges under the best conditions, minimizing degradation. Fast charging leads to up to 1.6% battery degradation every 100 days, according to an experiment comparing 5W and 25W charging on six identical smartphone batteries.

Sorry but that’s not the correct conclusion (or advice). Fast charging to 80% at cool temperatures will give a much better lifespan than charging slowly to 100% in a warm room. The issue isn’t charging speed, it’s the heat, along with time of strain (at high SOC). In fact there are pulsed very high speed charging patterns under testing that show even lesser dendrite formation than standard charging.

For anyone wanting to learn more, I highly recommend battery university. They’re probably the best resource out there on the net for genera purpose info on lithium batteries.

by user_7832

4/23/2025 at 11:23:50 AM

> Fast charging to 80% at cool temperatures will give a much better lifespan than charging slowly to 100% in a warm room.

How low do you suggest I should put the temperature in my bedroom, so that my phone would be comfortable fast charging?

by maratc

4/23/2025 at 10:05:07 PM

Anything around 20 degC ambient temperature should be fine. More important is that the phone can easily dissipate heat. It should not be covered by blanket or near a heater or in direct sunlight.

by seb1204

4/24/2025 at 10:22:55 AM

I guess you've missed my point, which is: I don't work for my phone. My phone works for me. As such, I shouldn't find myself in the situations where I have to create the optimal conditions for my phone, but rather my phone should somehow accommodate the conditions that I deem optimal for me. The idea that somehow I should provide "cool temperatures" in order to "give a much better lifespan" to my phone while it is "fast charging" ... seems completely idiotic to me. Cooling my room to 20C all year round will incur huge electricity costs, but even if the cost was zero, I don't work for my phone. The other options -- whether slow charge, or replacing the battery, or replacing the phone -- render the option of cooling my home inconvenient to the extreme.

by maratc

4/23/2025 at 1:12:53 AM

Wish they’d kept 12V throughout the PD standards. So useful for hobby stuff

by Havoc

4/23/2025 at 8:59:11 AM

You may already know this but getting 12V out of a 15V PD is relatively straightforward with either a linear regulator (less ripple but less efficient) or a buck converter (more ripple but more efficient). The Internet is full of very inexpensive boards that do all that.

by nicolaslem

4/23/2025 at 3:26:16 PM

Yeah I'm usually doing one conversion already (think 12v fan + 5v/3.3 esp32) so ideal case for me is pull 12 for the fan since that's the bulk of current and convert that down for esp/pwm but many ways to skin that cat I suppose.

I have discovered that certain Anker chargers are happy to supply 12V PD though...and it tends to be their cheaper charger lines. e.g. A2149 while the more expensive ones refuse 12V requests

by Havoc

4/23/2025 at 8:37:49 AM

I disagree. 12 V is not that much for an adult when you put it on your tongue, but with today's ubiquitous technology in everything, a toddler that puts everything in his mouth, will lead to a lot of distress and fears. I prefer the existing 5V. I suspect you are young and still not a parent.

Also, as a hobbyist, you can pretty much get a cheap PC power supply and transform it in a very professional "every volt and power under the sun" power supply for your hobbies. That's what I did.

by unnouinceput

4/23/2025 at 8:50:23 AM

This does not make sense as PD needs to negotiate with the device to get anything more than 5V. Putting random cables in your mouth won't result in getting 12V or even the 48V that PD can output.

by nicolaslem

4/23/2025 at 9:10:38 AM

> I disagree. 12 V is not that much for an adult when you put it on your tongue, but with today's ubiquitous technology in everything, a toddler that puts everything in his mouth, will lead to a lot of distress and fears. I prefer the existing 5V.

But PD not only already has 20V (or 19?) which can do everything 12V can, but I hear there's a new standard for going above 100W, which, presumably, works at an even higher voltage. Not sure how removing 12V specifically helps with the situation you describe.

by vladvasiliu

4/23/2025 at 11:09:31 AM

Yep, it's even mentioned in the article - it's maximum of 48V @ 5A for total of 240W.

by izacus

4/23/2025 at 9:36:19 AM

This comment is incredibly rude and patronizing. Many young people are parents and many older people are not.

also that's not how USB-PD works...

by mog_dev

4/23/2025 at 4:36:24 PM

>I prefer the existing 5V.

Guess what USB-C PD defaults to when you put in on your tongue. Low current 5V. ;)

Most PSUs will happily send 50-100 watt down the 5V line to anything that's connected including childrens tongues while usb-c will top out at 15W without negotiation

So maybe spare me the misinformed lecture about what is safe...

by Havoc

4/22/2025 at 10:00:36 PM

Today, a charger is a full-fledged computer with more processing power than the Apollo 11 spacecraft that brought humans to the Moon. Before the charging adapter starts pumping the voltage, it must first communicate with the smartphone. Incompatibility of the communication software protocol is the reason why a smartphone with USB PD, for example, cannot fast charge from a VOOC charger.

Read on technical details of fast charging technologies. Find out why the best charger – is your old feature phone's charger.

by uycyp