Battery Life Meter

It does a little of everything. Mostly it's building an estimation model for how much charge is left based on how much current is used, how much current goes in, temperature, etc. It's not a simple calculation based on internal resistance, voltage, current, etc. It's constantly monitoring what the battery is doing to determine how much estimated charge is left.

There are a lot of little things that go into calculating how much estimated charge there is, as well as estimating what the remaining capacity is. It can be off sometimes, which is why some people with older batteries see a sudden jump in charge level.

mcewans wrote:

It’s close to the other battery life monitors on the App Store. On my phone the Apple monitor reads 97% and the other apps read 100%.

Oh - you meant the battery health? It's a lot of little things that are used to calculate the battery health. However, the one thing that may change that reading is the temperature. I use coconutBattery to check the battery health, and recently I've seen anything from 92% to 97%. I always get the highest health reading if I've placed it in a warm spot like my pocket before I check.