Battery life

some myth on how one treat batteries can cause damage to them

try reading

Batteries - Maximizing Performance - Apple

Over time, phone batteries hold less charge. If your phone is older, get the battery changed, upgrade, or Check what apps are using a lot of battery in settings. If you have a new phone, check if any apps are using abnormal power, and If not, STOP USING IT IMMEDIATELY, the battery may be bulging, which can be extremely dangerous.