Security System Backup Battery Calculator
Estimate security system backup battery amp-hour demand from entered standby and alarm loads, durations, and capacity reserve.
Enter system load and duration
Required usable capacity
About this calculator
Estimate usable battery capacity for a security system using entered system-level standby current, alarm-period current, and their durations. A user-entered reserve is applied to the total amp-hour demand.
Use the operating durations and load schedules established for the specific security system.
Method and assumptions
Standby demand = standby current × standby hours. Alarm demand = alarm-period current × alarm hours. Estimated required capacity = (standby demand + alarm demand) × (1 + reserve percentage ÷ 100).
Each current is treated as constant throughout its period. Battery discharge performance, end voltage, temperature, age, charger limits, and equipment-specific requirements must be reviewed separately.
FAQs
Should alarm current include the standby load?
Enter the total current drawn during the alarm period, including equipment that remains active. Do not add the standby load a second time unless it is excluded from that alarm-period total.
Does this determine the required backup duration?
No. Enter durations established by the security system design, contract, and applicable requirements. Fire alarm rules may differ and are not evaluated here.
Sources
Use the security equipment load schedule and manufacturer specifications for current, battery, charger, and discharge data.