Battery capacity, loop voltage drop, and detector spacing — all aligned to current British Standards.
BS 5839-1:2025
Estimate the minimum battery capacity required for a fire alarm system per BS 5839-1:2025.
Usually 24h (non-domestic) or 72h (high-risk/remote)
Usually 30 min for most premises
Total quiescent current of all devices
Total current when all sounders active
Result
Standby Capacity
3.60 Ah
Alarm Capacity
0.40 Ah
Recommended (×1.25)
5.00 Ah
BS 5839-1 requires a 25% capacity margin. Always verify against manufacturer data sheets.
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