Battery capacity is the total amount of electrical charge or energy a battery can store and deliver under specific test conditions.

• Ampere-hours (Ah) or Milliampere-hours (mAh): Measures electric charge capacity—how many amps (or milliamps) the battery can supply for one hour before it discharges (e.g., 1 Ah = 1,000 mAh).

• Watt-hours (Wh) or Kilowatt-hours (kWh): Measures total energy capacity. You calculate it by multiplying the charge capacity (Ah) by the battery's nominal voltage (V):
                             

                                    Energy (Wh)= Capacity (Ah) x Voltage

• The Fuel Tank Analogy: Capacity works just like a car's fuel tank—a larger capacity means more stored energy and a longer runtime or driving range before you need to recharge.

• Charge vs. Energy: An Ah or mAh rating only tells you the electrical charge; to compare different battery chemistries or voltages accurately, use Watt-hours (Wh).

• Discharge Rate: Drawing power too quickly lowers the usable capacity because chemical reactions inside the battery cannot keep up.

• Temperature: Cold temperatures reduce deliverable capacity and internal efficiency, while excessive heat can degrade long-term battery health.

• Aging and Depth of Discharge (DoD): Repeatedly draining a battery past its recommended limit (or general wear over time) reduces its overall State-of-Health (SOH) and maximum capacity.