Solar Battery & Backup Calculator
Plan battery backup for load-shedding or night-time use. Enter the load you want to run and for how long; choose lithium or tubular batteries.
Updated
Results are estimates for planning. Actual figures depend on local conditions, prices and quotes — verify before making decisions.
Formula
Energy needed (Wh) = Load (W) × Hours ÷ Inverter efficiency
Battery capacity (Wh) = Energy ÷ Usable depth of discharge
Ah = Capacity ÷ System voltage
Lead-acid/tubular batteries should only be discharged about 50% for a long life; lithium (LiFePO4) can safely use about 80–90%.
Examples
800 W for 5 h, lithium, 24 V
You need about 206 Ah at 24 V — 4 × 12 V 200 Ah batteries
500 W for 4 h, tubular, 12 V
You need about 370 Ah at 12 V — 2 × 12 V 200 Ah batteries
Important information
- Battery capacity falls in hot rooms and with age; keep batteries ventilated and add 10–20% margin.
- Batteries in series must be the same type, age and capacity.
Frequently asked questions
How many batteries do I need for a 1 kW load?
For 4 hours on a 24 V system with lithium (90% usable) and a 90% efficient inverter: about 4.94 kWh, or 206 Ah at 24 V — two 12 V 200 Ah batteries in series is not quite enough, so you would use four (2 × 2).
Lithium or tubular?
Lithium costs more upfront but lasts many more cycles, charges faster and lets you use more of its capacity. Tubular is cheaper but heavier with shorter life.
What system voltage should I choose?
12 V suits small UPS systems, 24 V mid-size homes, and 48 V larger hybrid systems (lower current, thinner cables).
Learn more
- How Many Solar Panels Do I Need? (Pakistan) — Size a home solar system from your electricity bill, understand peak sun hours and efficiency, and estimate payback.
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