The quantity of electrical energy stored within a battery, measurable in units such as Ampere-hours (Ah) or milliampere-hours (mAh), represents its capacity to deliver electrical current over a period of time. A fully energized battery possesses the maximum designed capacity, while a depleted battery is incapable of supplying sufficient current to power a connected device. For instance, a battery rated at 2000 mAh can theoretically supply 2000 milliamperes of current for one hour, or proportionally less current for a longer duration.
This electrical energy reserve is fundamental to the operation of countless portable and stationary devices. It allows for autonomous functionality in items ranging from mobile phones and laptops to electric vehicles and backup power systems. The ability to store and release electrical energy on demand provides independence from direct power sources, enabling mobility and uninterrupted operation during power outages. Historically, advancements in battery technology, which have progressively enhanced this stored energy capacity and lifespan, have significantly impacted technological development and societal convenience.