Studio Matrx Monthly · Volume 1 · Issue 2 · July 2026
Amogh N P
 In loving memory of Amogh N P — Architect · Designer · Visionary 
Alarm standby battery sizing

Alarm Battery Backup Calculator

A burglar-alarm panel’s standby battery has to keep the system alive through a mains cut and still have enough left to drive the sirens when it triggers. Enter the panel’s quiescent draw, the hold-up hours you need, the siren current and how long it must sound to get the required battery amp-hours — and the next standard size to fit. Planning figures; runs in your browser.

Battery chemistry (usable capacity)
Batteries are never fully usable and fade with age — we derate to stay honest. Lithium tolerates a deeper discharge.
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Required battery capacity
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Standby Ah
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Alarm Ah
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Fit at least (Ah)
Holding 150 mA for 24 h of standby, plus 1000 mA of siren for 30 min, on a sealed lead-acid (0.7) battery needs about 5.9 Ah. Fit at least a 7 Ah battery.

Planning estimate only — the required standby time is set by your installer or insurer, so confirm it rather than trusting a default. Sealed lead-acid batteries fade and are best replaced every 3–5 years; a dead standby battery means no protection during a cut, so test under load and log the result. Verify against the panel and battery datasheets and a timed test.