Fire Alarm Battery Calculator

Calculate secondary power battery capacity for fire alarm systems per NFPA 72 requirements.

System Type

Standby Duration Required (hours)

Alarm Duration Required (minutes)

Panel Standby Current (mA) From panel specifications - typically 100-300 mA

Panel Alarm Current (mA)

Number of Initiating Devices

Avg Current per Device (mA) Typical smoke detector: 0.2-0.5 mA standby

Number of NAC Circuits

NAC Alarm Current per Circuit (mA) Total load per NAC circuit during alarm

Additional Relay/Aux Loads (mA)

Battery Requirements

Minimum Battery Capacity

Panel Standby -

Device Load -

Auxiliary Loads -

Total Standby Current -

Standby Amp-Hours -

Panel Alarm -

NAC Load (all circuits) -

Total Alarm Current -

Alarm Amp-Hours -

Calculated Capacity -

With 20% Safety Factor -

Recommended Battery -

Add 20% to calculated capacity to account for battery aging and temperature variations. Batteries lose capacity over time.

Common 12V SLA batteries: 7AH, 12AH, 18AH, 26AH, 33AH, 40AH, 55AH, 75AH, 100AH. Select next size up from calculated.

NFPA 72 requires full recharge within 48 hours. Charger must be sized appropriately for battery capacity.