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NFPA 72 §10.6.7
Standby & Alarm Battery Calculator
Size the secondary battery from the system's standby and alarm current draw.
Enter the system's current draw to see the required battery capacity.
NFPA 72 raised this factor from 1.20 to 1.25 in the 2022 edition (§10.6.7.2.14). Pick the edition your jurisdiction has adopted.
Sealed lead-acid capacity drops well below its 77°F rating in cold ambient — manufacturer curves commonly show roughly half capacity or less near 0°F. Pull the exact percentage from your battery's datasheet for the coldest temperature the battery will actually see, and enter it here. Leave blank if the battery stays near room temperature.
A necessary note. The battery formula and standby/alarm durations follow NFPA 72
§10.6.7.2.1 and §10.6.7.3; the aging safety factor change is per §10.6.7.2.14 (2022
edition). This tool is a planning aid, not a substitute for a code review by a licensed design
professional or your authority having jurisdiction, and it does not replace the manufacturer's own
battery calculation for the specific panel and battery installed.