Battery Sizing Calculator

AS 1851-2012 Appendix F – Fire Alarm Panel Batteries

Standby (Quiescent) Load

Quiescent Current, I₀ ?

Current Units

Standby Time, T₀ (hours) ?

24h standard • 48h critical • 72h high-security

Alarm Load

Alarm Current, I_A ?

Current Units

Alarm Time, T_A (hours) ?

0.5h (30 min) standard per AS 1670.1

Capacity Factors

De-rating Factor, F_c ?

2.0 standard for ≤1 CIE connected

Compensation Factor, L ?

Temperature Consideration ?

Installed Battery (Optional)

Installed Battery Capacity (Ah)

Enter to check pass/fail

Required Battery Capacity

Required Capacity

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Status

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Calculation Breakdown

Standby: I₀ × T₀ —

Alarm: F_c × I_A × T_A —

Subtotal (before L) —

Required: Subtotal × L —

Formula: C₂₀ = L × [(I₀ × T₀) + F_c × (I_A × T_A)]

Save Calculation

Common SLA Battery Sizes

Capacity	Typical Use	Dimensions (approx)
1.2 Ah	Small panels	97 × 43 × 52 mm
2.2 Ah	Light duty	178 × 34 × 60 mm
4.0 Ah	Medium panels	90 × 70 × 101 mm
7.0 / 7.2 Ah	Standard	151 × 65 × 94 mm
12 Ah	Larger systems	151 × 98 × 95 mm
17 Ah	Heavy duty	181 × 76 × 167 mm
24 Ah	Large installations	166 × 175 × 125 mm

Always verify physical dimensions fit enclosure.

Standards Reference

AS 1851-2012 – Routine service of fire protection systems and equipment (Appendix F)

AS 1670.1 – Fire detection, warning, control and intercom systems

AS 1670.4 – Sound systems and intercom equipment

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