Fire Alarm Battery Sizing

Preliminary sizing aid only. This tool applies the standard NFPA 72 §10.6.7.2 battery formula and the code-edition correction factor (1.20 pre-2022 / 1.25 for 2022 and later, per §10.6.7.2.14) that you select. It does not include a manufacturer device database — enter standby/alarm current per device from the actual datasheet. Final battery calculations must be documented and submitted per the AHJ's requirements and reviewed by a qualified fire alarm professional against the specific control panel/power supply manufacturer's own battery calculation worksheet.

System & Code BasisTag, system type, code edition, standby time

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Project / panel tag System type Code edition

Qualified emergency generator present (standby time may reduce to 4h)

Device LoadsStandby & alarm current per device group

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Label Qty

Standby current, each (mA) Alarm current, each (mA)

Margins & Charger Check (optional)Extra derating and 48-hour recharge verification

Additional margin (%, aging/temperature) Charger rated recharge current (A)

Result — Required Battery

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Ah required

Recommended battery size

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Correction factor applied

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Total standby current

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Total alarm current

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Standby time used

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Alarm time used

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Include Calculation Ledger in report Include OhmZone brand mark in report

Report template (.docx, optional)

Calculation Ledger

clause-by-clause

Device Load Summary

Label	Qty	Standby (mA ea.)	Alarm (mA ea.)	Standby total	Alarm total