Battery capacity refers to the amount of electrical energy a battery can store, typically measured in ampere-hours (Ah) or milliampere-hours (mAh). This measurement indicates how long a battery can power a device before needing to be recharged. A higher capacity means the battery can run a device for a longer period. For example, a smartphone battery with a capacity of 3000 mAh can generally last longer than one with 2000 mAh, assuming both phones use similar power. Understanding battery capacity is essential for choosing the right battery for devices like laptops, smartphones, and electric vehicles.