The storage capacity of a battery is designated by which unit?

• A. A kilowatt-hour
• B. An amp-hour
• C. A standard operating condition
• D. A maximum point power

Answer: (B)

Battery storage capacity is expressed in amp-hours because it represents the amount of charge stored and how long a certain current can be drawn from the battery. An amp-hour means the battery can deliver 1 amp for 1 hour (more generally, current times time). So a 50 Ah battery can supply 1 A for about 50 hours, or 5 A for about 10 hours, neglecting losses. This is different from kilowatt-hours, which measure total energy (voltage times amp-hours) the battery can supply, not just the charge stored. The other options aren’t units of capacity: a standard operating condition is a test reference, and maximum point power isn’t a standard unit of capacity.