Battery Backup Sizing Calculator

Based on AS/NZS 3011 design methodology for electronic security applications

System Parameters Step 1

Battery Chemistry * i

System Voltage *

Load Current * i

Required Backup Time * i

Derating Factors Step 2

Depth of Discharge (DoD) i

50%

Recommended max for SLA in standby applications

System Efficiency Loss i

15%

Charger & conversion losses (typically 10–15%)

Temperature Derating (optional)

Ambient Temperature i

25°C

✓ Nominal — no derating applied

Battery capacity is rated at 25°C. Derating is applied automatically for temperatures outside 20–30°C.

Calculation Breakdown

Three-Step Sizing Method (per AS/NZS 3011)

Calculate baseline capacity (no losses)

Base Ah = Load (A) × Runtime (h)

—

Apply system efficiency losses

Adjusted Ah = Base Ah ÷ (1 − loss%)

—

Apply Depth of Discharge limit

Min Battery Ah = Adjusted Ah ÷ DoD%

—

Suggested Battery Configurations

* Parallel connections increase Ah capacity (same voltage). Series connections increase voltage. Always verify configuration compatibility with your DC-UPS model.

Reference Table — 12V SLA Backup Times

Estimated backup times for common SLA battery sizes. Assumes 50% DoD and 15% system losses at 25°C. Your calculated load is highlighted.

Load (A)	Battery (Ah)	Usable Ah *	Backup Time (h)

* Usable capacity = Battery Ah × 50% DoD × (1 – 0.15 loss factor)

⚠ Important: Results are indicative only and based on the parameters entered. Always verify against actual device datasheets, apply appropriate temperature and voltage-drop derating for your installation environment, and ensure compliance with AS/NZS 3011, AS/NZS 2201.1, and AS/NZS 3000. Battery sizing must be based on the full design load — never the diversified load.

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