In what units is battery capacity expressed?

• A. Ampere-hours
• B. Watt-hours
• C. Volt-amperes
• D. Coulomb-seconds

Answer: (A)

Battery capacity is the total electrical charge stored, i.e., how much current the battery can supply over time. Ampere-hours expresses this as current times time, so a rating like 5 Ah means you could draw 5 amperes for 1 hour, or 1 ampere for 5 hours. This makes ampere-hours a practical way to judge how long a battery can power aircraft systems under load. Energy content is described in watt-hours, which is voltage times amp-hours (Wh = V × Ah) and reflects the total energy available, not just the charge. The other units describe different quantities: watt-hours is energy, not capacity; volt-amperes is apparent power, not stored charge; and coulomb-seconds isn’t a standard unit used for battery capacity.