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UPS Battery Backup Sizing

Standby Runtime · Ah Sizing · Security Loads

When to use: Size standby batteries for a security panel, NVR, and access-control gear. Battery Ah = (load watts × runtime hours / efficiency / system voltage) / usable depth-of-discharge. UL 294 / NFPA 72 typically require 4 hours standby for access control and fire-integrated systems; verify the AHJ requirement for your occupancy.

System
min
Inverter + losses
%
SLA ≈ 80%
%
Backed-Up Loads
W
W
W
Required Battery Capacity
122.5
Ah at 12 V — use ≥ 150 Ah SLA
Results
Total Load250 W (278 VA)
Energy over Runtime1176 Wh
Required Capacity122.5 Ah
Standard Battery150 Ah
Runtime240 min
Notes
Ah = (W × h / eff / V) / usable DoD
UL 294 / NFPA 72 often require 4-hour standby
Peukert effect reduces SLA capacity at high discharge
Derate battery capacity ~20% for end-of-life and cold