A battery is a device containing single or multiple cells that convert chemical energy into electrical energy. An aircraft has a main battery and auxiliary power unit (APU) battery. The main battery activates the aircraft even before the aircraft engine has started. Main batteries are also used in refueling the plane. The main battery provides backup power to the aircraft in case of emergency power failure. Aircraft batteries help to power the electrical system in an aircraft. When the APU or engine starts, they drive the aircraft generator which power the aircraft’s electrical system and also recharges the aircraft batteries. APU also acts as redundancies in case of emergency power failure. Lithium ion batteries are used in main and APU batteries. These batteries are made of eight cells that produce ~32-V DC. Lithium ion batteries contain redundancies that help the aircraft to fly even in case of battery fault. Rising demand for lithium ion based battery compared to nickel cadmi...