I am aware that the Android OS when calculating time left it cannot really calculate true usage, and an A.I. algorithm that would learn how you use your phone and give better estimations would actually deplete the battery on it's own.
On the other hand though. When giving time left estimations what does it check? Does it check the remaining percentage or the remaining milliamps? Because a phone with 4000 milliamps at 50% will probably have the same battery life left than a phone with 2000 milliamps at 100%
So what does it really check to do the calculations?