Why Does the Phone Drain Its Battery Even When It Is Not In Use? Why Does the Phone Drain Its Battery Even When It Is Not In Use? It is caused by battery deterioration due to improper use or aging of the battery due to long-term use. Of course, it doesn't end there. Charging Cycle: Batteries only have a certain lifespan measured by charging cycles. This means that smartphone batteries are only fully charged and discharged a certain number of times. […]