Myth 1: Killing background apps extends battery life
Killing background apps will not extend your battery life. Those apps are effectively “frozen” in the background and, according to Apple multitasking does not put unnecessary strain on the battery.
Myth 2: Letting your battery die extends battery life
It’s impossible to physically measure how much power remains in a battery. Because of this, mobile device manufacturers have developed sophisticated algorithms to estimate the remaining charge. Still, over time the reading will begin to drift away from the actual value. Using the phone until it dies then charging it to 100% (calibrating) helps snap these readings back into place. It does not, however, extend battery life; it mainly makes the indicator more accurately reflect the battery’s state. Apple advises users to calibrate monthly, but any more often is overkill. In practice you shouldn’t have to worry about this too much if you’re using your phone regularly.
Myth 3: Overcharging will damage batteries
While overcharging is a concern for gadgets that use lithium ion batteries, Apple has built-in protections to keep these things from affecting iOS devices. When the battery fills up, the phone will let it drain to 99%, then fill back up. This cycle will repeat as long as the phone is charging, although the battery indicator will report “full” rather than reflecting the actual fluctuating charge to avoid distracting users. Likewise with letting the battery “die” too often.
What will damage batteries, however, is letting the phone die and then tossing it into a drawer for two months. Batteries lose charge over time even when not in use, and letting the battery sit with little to no charge will cause it to lose capacity.