How long will back up battery last?

How long will back up battery last?

• A. 4 hours
• B. 2 hours
• C. 6 hours
• D. 8 hours

Answer: (A)

Estimating how long a backup battery lasts comes down to comparing stored energy with energy use. The battery’s capacity is the amount of energy it can provide, usually given in watt-hours (Wh) or as amp-hours (Ah) at a certain voltage. The device or system power draw is the rate at which that energy is used, in watts (W). The rough running time is: runtime (hours) ≈ battery watt-hours ÷ load watts If you have capacity in Ah and voltage, convert to watt-hours by multiplying Ah × voltage. Real-world factors like inverter efficiency, temperature, battery age, and how deeply you discharge the battery will reduce the actual time. Example: a 4 Ah battery at 12 V has about 48 Wh. If the connected equipment draws 12 W, the expected runtime is 48 ÷ 12 = 4 hours. If the load were 24 W, it would be about 2 hours; at 8 W, about 6 hours; at 6 W, about 8 hours. For this question, the backup battery lasts four hours because the given or typical scenario yields a 48 Wh capacity with a 12 W draw, giving 4 hours of operation.

Estimating how long a backup battery lasts comes down to comparing stored energy with energy use. The battery’s capacity is the amount of energy it can provide, usually given in watt-hours (Wh) or as amp-hours (Ah) at a certain voltage. The device or system power draw is the rate at which that energy is used, in watts (W). The rough running time is:

runtime (hours) ≈ battery watt-hours ÷ load watts

If you have capacity in Ah and voltage, convert to watt-hours by multiplying Ah × voltage. Real-world factors like inverter efficiency, temperature, battery age, and how deeply you discharge the battery will reduce the actual time.

Example: a 4 Ah battery at 12 V has about 48 Wh. If the connected equipment draws 12 W, the expected runtime is 48 ÷ 12 = 4 hours. If the load were 24 W, it would be about 2 hours; at 8 W, about 6 hours; at 6 W, about 8 hours.

For this question, the backup battery lasts four hours because the given or typical scenario yields a 48 Wh capacity with a 12 W draw, giving 4 hours of operation.