iPad Charging iPad with high-output charger = battery strain??

[Beliblis]

Hi,

For convenience, I often charge my iPad Pro with my Macbook Pro's charger. The MBP charger obviously has a higher output.
Does this potentially reduce the life of my iPad's battery? Or is the "charger input" somehow throttled anyway, so that it won't matter?

Likewise: is it benefitial for battery-life to use a low-output 1-2A charger overnight, to charge the iPad?
And is it possible to set the iPad to only charge up to 80%? (Apparently, going 0-100-0 all the time reduces lithium batteries lifetime)

Many thanks!

 

[JPack]

You generally want to minimize heat when charging to maintain battery health. As long as the iPad doesn't feel warm, you should be fine.

 

[wilberforce]

The iPad should manage its charging rate such that it does not accept current at a too high a rate, regardless of the size of the charger. This is kind of the whole point of being able to universally charge via USB-C, from any charger to any device, the user does not have to actively manage it. You could test this, by comparing charge time on the two chargers.

It is not possible to set it to charge only up to 80%, which is unfortunate, as you are correct: maintaining charge above 80% reduces the life. (Actually, technically it is maintaining the battery voltage high that reduces the life, but device manufacturers allow the batteries to be charged to a high voltage to squeeze as much runtime as possible out of the battery.) However, apparently Apple has a "charge management feature" to mitigate this:

About iPad and iPhone Charge Management feature - Apple Support

iPadOS and iOS include a charge-management feature to maintain battery health when iPad or iPhone XS, iPhone XS Max, iPhone XR, or later is connected to power for prolonged periods of time.

support.apple.com

The recommended charge rate for preserving life of Li-ion batteries is 0.8C, where C is the charge rate such that it fully charges in 1 hour. In other words, the charge rate at any time should not exceed the rate, when extrapolated, that would charge it from 0-100% in 75 minutes. As it is unlikely that your normal charger charges this fast anyway, using a smaller charger will likely have limited benefit.
A exception might be if you are in a particularly hot environment (like in a car in hot sun). High temperature is bad for batteries, and charging at lower rate would then be better, as it would lessen the temperature rise in the battery.

Learn About Batteries

Battery University™ is a free educational website offering hands-on battery information.

batteryuniversity.com

TL,DR: don't worry about it.

 

[Digitalguy]

The iPad pro with a Macbook charger will charge at around 30watts, which will create more heat that 10-12watts or even 18-20watts... This has an impact of battery health, but less so on the 12.9in which has a larger battery.
The 80% figure is just an arbitrary threshold. Batteries don't like very high and low voltage and live the longest at nominal voltage. But the issue is not charging to 100% but leaving it for hours at 100% (for instance by leaving it plugged in or charging it at night).
If you charge it at 100% and then use it, that's perfectly fine.
Personally I set a shortcut warning me when charges goes above 90% and below 50%.

 

[Beliblis]

Thanks for your replies! Very interesting!
I tested charging times today, starting at 2% battery life.
@wilberforce The Macbook charger charges the small iPad Pro for 65% within 45min. So I guess that's just about the limit, and I'll try charging with my standard charger as often as possible.

@Digitalguy If iit's better not to leave the iPad at 100% and plugged in, that would mean using up a lot more charge cycles – which in turn reduces battery life as well. Most days, I can go through a whole iPad charge, meaning: 365 charge cycles per year if I don't leave it plugged in...
Wouldn't it be better to leave it connected to a low output USB charger whenever possible? Or at least some sort of 'random' charge pattern / leaving it 100% charged/connected to USB oevery other day or so?

 

[Digitalguy]

Thanks for your replies! Very interesting!
.

@Digitalguy If iit's better not to leave the iPad at 100% and plugged in, that would mean using up a lot more charge cycles – which in turn reduces battery life as well. Most days, I can go through a whole iPad charge, meaning: 365 charge cycles per year if I don't leave it plugged in...
Wouldn't it be better to leave it connected to a low output USB charger whenever possible? Or at least some sort of 'random' charge pattern / leaving it 100% charged/connected to USB oevery other day or so?

The importance of charge cycles should be de-emphasized. You can have 2 identical devices, one with 800 cycles and one with 10 and the 800 one has better battery health (I had exactly that, the 800 has 93% health, the 10 cycle one 82%), simply because the 800 cycles were "good cycles" (for instance avoiding extremely low or high voltages) and the 10 cycles were just the result of it being plugged in (or completely dead) 98% of the time....
Leaving the iPad plugged in does NOT use up any cycle (because the counter will not take into account cycles if the battery stays at 100%, even if it trickle charges), but can wear the battery more than good cycles, because of the effect of high voltage on batteries.
The worst situation is bad cycles (cycles from 0 to 100 where the iPad stays for prolonged periods at 100 or, worse, at 0).
The situation in the middle is cycling from 0 to 100 but not leaving the iPad dead or plugged in for prolonged periods.
Low output chargers make NO difference at all. Once the voltage is high, even the most powerful chargers will slow down the charge to a low level anyway and will just trickle charge like any other charger.

 

[Beliblis]

@Digitalguy Thanks for the explanation.
Last questions (which we haven't covered yet... since you know your stuff about batteries): Do you know if it's possible to increase battery health at all? For example with a dedicated / bespoke charge pattern over several weeks?
In the old days (some of the first NiMH AA batteries), some people claimed it was possible to 'service' worn-out AA batteries by putting them in the freezer before charging. Can't remember if it really worked or not... in hindsight it seems to be an urban legend to me.

(Not that I would want to put my iPad into the freezer of course

 

[Digitalguy]

@Digitalguy Thanks for the explanation.
Last questions (which we haven't covered yet... since you know your stuff about batteries): Do you know if it's possible to increase battery health at all? For example with a dedicated / bespoke charge pattern over several weeks?
In the old days (some of the first NiMH AA batteries), some people claimed it was possible to 'service' worn-out AA batteries by putting them in the freezer before charging. Can't remember if it really worked or not... in hindsight it seems to be an urban legend to me.

(Not that I would want to put my iPad into the freezer of course

Yes, it is possible to "repair" the battery degradation, but it's not something you could do on your own. There are some startups are specialising in restoring the original capacity of a batteries (I know a guy who works in one of them), but it's a complex and relatively expensive process that is worth only for large batteries like those of EVs (because it involves opening the battery and sort of "cleaning" the cells). So forget about doing that for consumer electronics.
The best you can do is doing "good" cycles, which to be honest is not always easy or comfortable if you only have one device. If you have several, it's much easier to set alerts at given battery levels (with either third party apps or Apple shortcuts) and use another device while one is charging.... There is no maximum number of cycles for a battery, it all depends on the quality of those cycles (maximum cycles given are only estimates, often based on full charge / discharge cycles). If cycled well and exposed to little heat, whether it's from hot weather or heavy workload (which is impossible in many laptops but possible with iPads depending on where you live) or from fast charging (best is to charge at 5v, regardless of the amperage, a 5v2ah or even 5v3ah will be much better for a battery than a 9Vx1,5ah), a battery, even used daily, could last for many years and still maintain a decent capacity (provided that the battery was made with good cells to begin)

 

[Beliblis]

Got it. So, coming back to how to best charge an iPad Pro:
According to apple, the iPad Pro's maximum supported fast charging rate is "18W (i.e., 12V @1.5A or 9V @2A)". The iPad Pro's original charger is 20W. I know W = V * A. But how does the iPad "choose" the voltage it receives from the power adapter? (Can't find my original charger at the moment, guess it's written on there?)
On the MBP 30W charger, there's 4 different V*A configurations.

An idea for overnight charging could be to do a shortcut with a homekit enabled socket, to turn off the socket as soon as battery reaches 90%. (I don't have any home kit sockets, so don't know for sure if this can be automated via Shortcuts).

 

[Digitalguy]

Got it. So, coming back to how to best charge an iPad Pro:
According to apple, the iPad Pro's maximum supported fast charging rate is "18W (i.e., 12V @1.5A or 9V @2A)". The iPad Pro's original charger is 20W. I know W = V * A. But how does the iPad "choose" the voltage it receives from the power adapter? (Can't find my original charger at the moment, guess it's written on there?)
On the MBP 30W charger, there's 4 different V*A configurations.

An idea for overnight charging could be to do a shortcut with a homekit enabled socket, to turn off the socket as soon as battery reaches 90%. (I don't have any home kit sockets, so don't know for sure if this can be automated via Shortcuts).

It's the power delivery protocol that will choose the voltage. The iPad pro supports 9V 2A and 15V 2A (since the iPad pro 2015, with the exception of the 9.7 pro). If the charger does not support 15V (like the one bundled with the USB C iPads) it will pick 9V (to be precise it will always briefly start at 5V and then negotiate the highest supported voltage by both the charger and the device).
The USB C iPad charger will charge at 9V 2A and the MacBook one at 15V 2A.
I don't do overnight charging for any device, but I know it's the most convenient way to charge for most people. So yes, what you mention is an option and one of the forum members does have a power socket that cuts the power.
Personally I use shortcuts to triggers alerts which is fine with me since I work from home most of the time.

 

[rui no onna]

An idea for overnight charging could be to do a shortcut with a homekit enabled socket, to turn off the socket as soon as battery reaches 90%. (I don't have any home kit sockets, so don't know for sure if this can be automated via Shortcuts).

Yes, it can. I have the 12.9” iPad plugged in for the entire workday at the office and use a Meross plug (with original Apple 20W charger) to keep the iPad between 60-80% charge.

At home though, I use a non-HomeKit TP-Link Smart Power Strip (with energy monitoring) plus Anker multiport charger so charging requires more manual intervention.

I have a shortcut setup to text me when the iPads/iPhones drop below 50% charge. Based on the text, I plug in devices for “overnight” charging. The plug/charger (5V/2.4A per port max) is scheduled to run from 2 AM to 5 AM which is when I wake up.

 

[phrehdd]

Rather curious to find out - there are multi-port GaN chargers that have become popular and some come with features that suggest they will smart charge devices such as phones, iPads, notebooks, etc. Does anyone know much about these chargers? Buzz words such as "PD 3.0" come to mind. Any takers?

 

[vince v.]

Hi everyone!
Very interesting discussion and that answered many of my questions.
I take this opportunity to ask one thing: are the same considerations valid when charging the iPad Pro through the USB-C port of the Magic Keyboard, perhaps with the 30W power supply?
(Sorry for any mistakes in my English)