Which battery rating is expressed in minutes?

The correct answer, reserve capacity, is the rating that indicates the duration a battery can deliver a specified amount of electrical current before its voltage drops to a level unsuitable for starting the engine or powering accessories. Specifically, reserve capacity is expressed in minutes, detailing how long the battery can maintain a steady discharge rate, commonly set at 25 amps, under controlled temperature conditions.

This measure is crucial for assessing how well a battery can support a vehicle’s electrical system during prolonged periods of discharging, such as when the engine is not running, and helps in determining the reliability of a battery under various conditions. In contrast, cold-cranking amperes (CCA) and cranking amperes (CA) are ratings focused on the battery's ability to deliver the necessary power to start a vehicle's engine, emphasizing high current output over a short duration rather than a temporal measure like reserve capacity. The battery voltage test assesses the voltage under various conditions but does not involve a time component in its rating.