It is advisable to apply the “40-80” rule, i.e. keep the battery charged between 40% and 80% at all times. You should therefore not wait for the phone to be completely flat to recharge it, nor charge it to 100%! Unlike old nickel batteries, lithium batteries better support short cycles, with several regular recharges.
Similarly, when you store your phone in the closet for a long time, it is better to store it with a 50% charged battery and then turn off the device, explains Apple.