How to size an inverter battery
To choose an inverter battery capacity you need two numbers: the total load you want to run (in watts) and the backup time you want (in hours).
1. Add up your load
List the appliances you want to run during a power cut and add their wattage. A few common examples:
- 1 LED TV: ~80 W
- 3 LED lights: ~30 W
- 2 ceiling fans: ~140 W
- 1 refrigerator: ~200 W (starting surge is higher)
2. Estimate the energy you need
Energy (Wh) = total load (W) × backup hours (h).
3. Convert to battery Ah
Battery Ah = (Energy in Wh) ÷ (battery voltage × depth of discharge × inverter efficiency).
For a 12 V tubular battery, a usable depth of discharge around 0.5 and an inverter efficiency around 0.8 is a reasonable starting point. This is an estimate; real backup depends on battery age, temperature and actual load.
4. Pick the next standard size
Battery capacities come in standard steps (for example 100 Ah, 120 Ah, 150 Ah, 180 Ah, 200 Ah, 220 Ah, 240 Ah). Choose the next size above your estimate rather than the exact figure.
Use the inverter-battery calculator on the home page for a quick estimate, then confirm the recommended model with a dealer.