My battery maximum capacity is at 84%.

I was wondering how low the maximum capacity could go could go before I start seeing problems of my phone shutting down.

It's an iPhone XS. Currently, at my usage, I can get through my whole day without any issues. I don't use the phone much and don't have many apps.

Are there warning signs that appear on this screen that appear when its too low?

Battery Screen of an iPhone XS

4 Answers 4


When your battery is actually suffering degraded performance, then the row labeled "Peak Performance Capability" will change to indicate it's no longer performing as well.

The percentage this occurs at is not set. Some iPhones will suffer symptoms earlier or later than others, depending on the size and chemistry of the battery.

The battery is not unsafe from a health perspective so long as no warnings appear in the settings app.


Apple has gone to extreme lengths to ensure that old batteries don't cause shutdowns.

Hence the whole "batterygate" thing, where Apple slowed down phones with old batteries so that high-usage power 'spikes' would never occur. (which is what causes shutdowns, as the battery can't supply the necessary power.)

When your capacity gets below 80%, you can go to an Apple Store and get a replacement battery. The fee is quite reasonable (varying with the size of your phone), and they can do it within an hour.

  • Alternatively, you can go to ifixit.com to buy battery and replace it yourself. Commented Apr 29 at 15:58
  • @VanitySlug-codidact.com In the UK, iFixit charge £47 for an iPhone X battery; and Apple charge £85, which includes a warranty. My time and the risk is well worth £38.
    – benwiggy
    Commented Apr 29 at 18:55
  • some people like living on the edge, man :) Commented Apr 30 at 13:04

It depends.

Some batteries keep even voltage and age to 20% capacity and run all the way smoothly.

Other have a problem with one cell and can’t even run the device when the overall capacity is 92%.

If you think of a battery as a gas tank, this lets you know how much of that tank original capacity is available for the next “fill”. Other characteristics determine if voltage is high enough so that diagnostic is more valid for sudden shutdowns due to low voltage even when there is plenty of mAH left in the “tank”.

The pragmatic thing to do is optimize your settings, make sure you have a backup, and watch things. Batteries are usually eligible for warranty service at 80 % FCC, but you can always get remote support from Apple to diagnose your battery health and decide when to get a repair.

  • Phone batteries are always single cell so they don't suffer from cell capacity mismatch or cell state of charge mismatch, like bigger batteries do. Unfortunately, all other aging and failure modes are possible..
    – fraxinus
    Commented Apr 28 at 15:15

The capacity degradation and the maximum discharge current decline (related to the peak performance property) are different things related to different aging processes.

This is why they don't happen at equal pace.

You may get a 90% capacity battery that fails the peak performance criteria (e.g. in cold climate)

- or -

as low as 65% max capacity battery that is still able to give off enough current when asked for (e.g. after heavy use in moderate conditions.

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