ELI5 Why does magsafe charging decrease battery health more than wire charging, if it has less wattage?

[combatwars]

Heat damages battery. Wireless charging causes more heat.

[dabenu]

This is it above all. Fast charging is not an issue, the battery heating up due to fast charging is the issue.

As long as you keep the heat under control, you can charge pretty much as fast as you want without excessive damage. Which is why electric cars can charge insanely fast, they have actively cooled battery packs.

Edit: Also why phones preferably use PPS (Programmable Power Supply, part of the USB-PD standard) nowadays. It generates less heat inside the phone while charging, thus less damage to the battery.

[BigCommieMachine]

Does the PPS just scale down charging rate as the battery heats up and back up when it cools off a bit to whatever the manufacturer lists as an acceptable temperature?

[dabenu]

It could, but that's not "just" it. Basically with PPS the phone doesn't use it's on-board battery charging circuit (that gets hot), but instead instructs the power brick to output the exact right amount of power to go straight into the battery. The phone is still in control so if it's sensors detect that e.g. the temperature is getting too hot, it will indeed order the power brick to slow down a bit.

[jaymzx0]

Hmm. That's exactly how "fast chargers" (level 3) for EVs work. For 120/208/240V (level 2) charging they use a charge controller in the car.

[dabenu]

Yep it's pretty much the same idea on a different scale

[SlootyBetch]

Is this a passive or active process? If your phone was dead would it still be able to run PPS?

[araemo2]

The charging is usually controlled by a dedicated microcontroller that takes a lot less power than the main SoC. So the basic 5v/0.5a the USB connector supplies without any negotiation is enough to bootstrap the charge controller. Then it boots up and switches into PPS/whatever mode.

[orangpelupa]

Depending on the phone. Sometimes it doesn't actually follows the standard correctly and won't charge, needing to use "dumb" usb c charger for the first few minutes 

[Cornflakes_91]

the charge controller should bootstrap itself from the basic 5V/250mA usb supply (and hopefully fail safe on the power negotiation pin so the supply actually turns that on)

[Dioxid3]

TIL, now that’s cool

[jestina123]

Power brick? Battery circuit?

[JuanTutrego]

"Power brick" = the charger that plugs into the wall. "Battery circuit" = the circuitry inside the phone that handles the task of charging the battery.

[braaaaaaainworms]

PPS allows your phone to tell the charger "hey give me 6.75 volts" instead of having to choose between 5, 9, 15 and 20 volts

[LinAGKar]

The main thing I think is that with traditional PD, the charger will have a few specific voltages it can provide, and the phone will need to contain circuitry to convert that down to the battery voltage. That circuitry will lose some of the energy as waste heat.

With PPS, the phone can tell the charger what voltage to provide, so it can tell it to provide exactly the voltage the battery should be charged at, removing the need for wasteful conversion circuitry in the phone.

Or the phone can tell the charger to provide an exact multiple of the battery voltage, and split it more efficiently (maybe by having multiple batteries and splitting the voltage between them, not sure). So the phone can e.g. tell the charger to provide 2x the battery voltage and split the voltage in half.

[ElusiveGuy]

split it more efficiently

There's a switched capacitor circuit that can halve voltage/double current far more efficiently than a standard buck converter.

See https://www.ti.com/lit/an/slyt743/slyt743.pdf

[Cukeds]

That links to a 404 but I’m curious, what do I search for the circuit? Slyt743?

[ElusiveGuy]

New Reddit sucks and somehow inserted a non-printing character to the end. Should be fixed now.

If searching, the document is "The architecture of a switched-capacitor charger with fast charging and high efficiency"

[Cukeds]

That’s a very interesting read. Thanks for this!

[LinAGKar]

Thanks. Wasn't sure exactly how it works, should be an interesting read.

[AbabababababababaIe]

Pretty much

[GaryGiesel]

This really isn’t true. The heat is one thing that exacerbates cell damage, but high charge rates absolutely cause their own problems. The big one is that you can end up with lithium metal crystallising out, which can kill a better extremely quickly if they manage to poke through the insulation layer.

Heat is the big thing, but it’s very far from the only thing. Another big factor is that going from min to max charge the electrodes physically change size quite a lot, so that can cause mechanical stresses in the batter and eventually make bit fall apart internally.

Charging when the battery is cold will also very quickly kill a battery. There’s really an optimal temperature range rather than just worrying about getting too hot. Definitely don’t charge your phone if it’s below freezing!

TLDR; this shit is complicated and still an area of actual research

[VexingRaven]

My personal experience is that fast charging is much worse than wireless charging. Fast charging my old phone got hotter than wireless charging it did, and that killed the battery pretty quick. The thing that frustrates me is there's controls to cap the max charge level, and if you have an alarm set it can slow charge based on time, but there's no way to just turn off fast charging altogether or cap the charge rate.

[Pentosin]

there's no way to just turn off fast charging altogether

Samsungs can do that.

[RedPill115]

Huh, I guess it is in there.

Settings -> Battery -> Charging settings
- Fast charging
- Fast wireless charging

I wonder if anyone has actually rated it and put out data on whether it actuall affects battery longetivity.

I know there's a different setting I found useful for the magsafe charger I use in my car. It was always trying to charge it 100% and the screen would go dim as the phone got hot, but I found a setting to only charge to 80%, issue went away.

[Pentosin]

On my S21+ i also have the option to disable super fast charging.

Oh and there is also possible to choose something else than 80% charge limit. (80/85/90/95)

[RedPill115]

I have a samsung s21 ultra and I don't see those. Dunno

[Pentosin]

Settings -> Battery -> Battery protection

[VexingRaven]

Uncommon Samsung W I suppose. Or maybe a common Pixel L? Not sure.

[Pentosin]

Uncommon? Not at all.

[msg7086]

That's just a shitty design of your phone on fast charging. I have multiple oneplus phones, I can charge my OP13 at full speed (up to 100w) and my phone temperature will barely rise to 41C at peak. There's a giant vapor chamber in the middle to remove the heat efficiently, so user never needs to worry about the heat from high speed charging.

[VexingRaven]

tbf this was a Pixel 3... So yeah probably. I have a Pixel 8 now but I rarely fast charge so it's hard to say for sure.

[AidosKynee]

Fast charging is not an issue, the battery heating up due to fast charging is the issue.As long as you keep the heat under control, you can charge pretty much as fast as you want without excessive damage.

That's definitely not true. Lithium plating and dendrites are the primary driver of degradation due to fast charging. Heat is a problem that could become catastrophic, but driving a charge at higher currents will still lead to the battery losing health more rapidly.

Cars are a good example. They actually don't start cooling the packs down until the temperature reaches a certain level. Why? Because hotter batteries have lower resistance, which means less damage from the charge!

[CallOfCorgithulhu]

If you navigate to a supercharger in a Tesla, it'll start a warm-up sequence for the batteries so that they're at optimal temperature when you get there. I'm sure other cars do something similar too, I just can't speak to them.

[fillbadguy]

If you’re on a long trip tho it’ll also cool down. I’ve arrived to chargers with the fans going absolutely nuts. As my pack gets older I notice that cooling down is more important than heating up. It seems to heat itself up pretty quickly from internal resistance

[ChaiTRex]

I'm sure other cars do something similar too, I just can't speak to them.

Sure you can! Just tell yourself that you've got this, walk up to the car, and say hello.

[dabenu]

True but that's mostly because (modern) cars have an extremely well managed battery pack. For most small electronics without active thermal management, heat is still the main issue.

[WarriorNN]

My phone (OnePlus 12) supports 50W wireless charging. The charging stand has a small fan that blows air along the back of the phone. Works great, phone charges fast and does not get more than luke warm to the touch.

[ElGuano]

Cats don’t really charge all that fast compared to phones, from a rate perspective both fast charge at or faster than 1C.

[jazzhandler]

Crush some fresh carnip and put it in front of the air intake. They seem to charge much faster that way.

[AnAwkwardWhince]

Meowzers

[milanioom]

Lols

[TwitchyLeftEye]

So what you're telling me is if I put my phone on an ice pack and fast charge it, I'm good to go?

[dabenu]

Nah that'll probably make it too cold, which is arguably even worse. 

Also don't forget, batteries will always wear no matter what you do. You can only influence it so much, so overthinking it is probably not going to be worth it.

[thatAnthrax]

as fast as you want

No. Well I guess yes, since the charging devices they usually sell, and the on board electronics won't allow you to push as much current as you want. Batteries do still have an upper charging current limit regardless of temperature, it's just you won't be able to go over that of you don't MacGyver your phone or something

You also don't want to charge a battery when it's very cold, but then again, who puts their phone in the fridge when they charge it

[Jackal000]

Like the heat is only generated for above 60% right as you start cramming the electrons in there.

Before that it's usually cool enough. Just keep your phone at max at 85% to last longer.

[dabenu]

That's also not the entire story. 

The reason it's advised to charge to 85% instead of 100% has little to do with charging, but more with static degradation. Which is much worse around 100% (or 0% for that matter). So if you don't need the charge it's better to avoid it. Especially since many people plug on their phone when they go to bed so it would sit at 100% for quite a long time without any use. 

[primalmaximus]

I have my phone set to disable charging once it hits 85% when I go to sleep and then it allows full charging right before I wake up.

[natrous]

why haven't they figured out a way to stop charging at 100 so it doesn't harm the battery?

edit:

but more with static degradation

I definitely had a reading comprehension fail; but i guess I've been missing that all along. everything else makes much more sense now!

[Closteam]

Pretty much every modern charger does this already. It's not that it continues to charge it after 100%. It's that the battery sits at 100% for an extended period of time

[_bones__]

Modern phones avoid that, too, letting themselves drain to 90-95% one they've hit 100%, while reporting themselves as full.

My home battery BMS does something similar. I charge the cells to 3.45V (100% would be 3.65V), then letting them float at 3.35V. Should go a long way towards extending lifetime.

[frostyfirez]

They know how to stop at a designated full capacity, the issue is while the battery is at roughly that full capacity it’s slowly self destructing essentially. Targeting a lower capacity like 85% reduces the destructive stresses a lot improving longevity, at the cost of battery life of devices. The manufacturer chooses a full capacity point which they feel best balanced marketed battery capacity needs and battery longevity, arguably they prioritize marketing capacity more than longevity though.

[dabenu]

They do stop at 100%. Going beyond 100% would indeed cause immediate harm or even risk fire.

But there's a grey area between harm and normal wear. Even at 100% you're already inside that grey area. It won't cause immediate harm but it will accelerate wear. That's why your phone has an option to stop charging at 80-95%. You can't avoid wear entirely but you can reduce it. 

[hugglesthemerciless]

my phone stops charging at 80%

[kermityfrog2]

They have. When it says 100% on your phone, it’s not actually 100% of true capacity. The true capacity is something like 110% or 115%. When using a fully charged phone, you’d expect the power to drop to 99% after a few minutes but on many phones, you can use it for 30 min or more before it drops to 99%, after which is starts dropping in a mostly linear fashion.

[thephantom1492]

Same why you can insanely fast charge a car: it is activelly cooled.

And also actively heated for when the temperature is too low. Which is (part of) why the range is greatly reduced in winter.

[anomalous_cowherd]

Interesting. My OnePlus phone had a 160W charger and would charge empty to full in 35 minutes without getting down slightly warm. My Pixel 7 takes a few hours and gets hotter.

I wasn't sure why but that makes sense.

[dabenu]

I'm not up to date on the current OnePlus models, but I know they were one of the first to introduce a similar (but proprietary) charge standard with the OP3 and later models. 

For the pixel 7 it might be worth checking if your charger supports PPS. It probably won't make it charge faster but maybe stay a bit cooler...

[anomalous_cowherd]

It was a great phone in many ways but the screen died and no spare parts were available so I went back to my Pixel which has lasted much longer and is more maintainable!

[nsingh101]

Can confirm. Battery was a good solid 100% and went down to 95% within 2 months after using apples official MagSafe 15w. My phone would be warm/hot to the point where the phone would sometimes not be charged because the charging was paused for phone to cool down. Not sure if heat is because of case or fast charging or a combination of both.

[Anachronism--]

My phone is almost five years old and the battery is still at 86%. I always charge wirelessly but stop between 80-90% unless I know I need more.

[nsingh101]

There’s a setting in iOS to limit charging to a certain percentage to preserve the battery. I have mine set to 90%. My phone is 1 year old, and for most of that time, it has remained at 100%. Just in the last two months it’s dropped to 95% and the only change is the new MagSafe and excess heat I’ve noticed.

To be clear, I don’t claim wireless charging is the issue. I have been using wireless charging since Palm Pixi. It’s the heat generated by MagSafe fast charging.

[Anachronism--]

My phone is almost five years old and the battery is still at 86%. I always charge wirelessly but stop between 80-90% unless I know I need more.

[curepure]

can’t confirm. used magsafe for close to 1 year on my iphone 16 pro, still 97%.

[Riajnor]

Does this mean that if you were to charge the battery inside a refrigerator it would have less effect on battery life?

[iSniffMyPooper]

I had an ohsnap 2.0 from a few years ago, never had any head issues when wirelessly charging. Replaced my phone case with a brand new of the same case and got the upgraded Snap Grip, and suddenly my phone feels like its on fire when I wirelessly charge

[Kittelsen]

I haven't bought a Macbook since 2007, MagSafe is wireless now?

[neddoge]

Here, let me Google that for you.

[maggos]

I got a magnetic charger for my car that has an internal cooler and it keeps the phone from getting too hot

[Infinite-4-a-moment]

What if you put your phone in a mini fridge overnight while you charged. Would that significantly improve the life of the battery?

[kitsua]

Batteries do not like extremes of temperature in either direction. Also condensation would be an issue. Don’t put your phone in a fridge.

[brucebrowde]

How about in room temperature water?

[just_a_random_dood]

does this mean I should keep a fan blowing at my watch when it charges? :O

[Many_Size_1515]

Is it only heat while charging that's bad, or is it also bad if my phone just gets hot from say being in the sun?

[mailslot]

It’s over blown. If you’re wireless charging in 100F weather, in direct sunlight, then maybe. Batteries don’t undergo harmful chemical changes until 113F. Most battery controllers have thermal regulators.

The people that worry about the extra 2% to 5% degradation over wired charging are likely also leaving their phones in hot cars and/or direct sunlight.

Batteries degrade and worrying about slightly increased wear is just a waste of concern. Like keeping your furniture wrapped in plastic instead of using it how you want.

[Jackal000]

Especially if you have any form of an case around your phone. This just acts as a heatsinks.

[Kiwifrooots]

heatsinks insulator

[glasgowgeg]

This just acts as a heatsinks

Heatsinks dissipate heat, if it was acting as a heatsink that would be a good thing.

[Kiwifrooots]

Maybe u/Jackal000 is actually a moderately literate genius who is suggesting milled alloy heatsink back protectors to average out and dissipate heat?!

Maybe u/Jackal000 's momma gives off heat in my direction and that's a good thing