Size an inverter battery from watts and hours
Battery voltage and amp-hours describe nominal energy. Usable energy also depends on chemistry, permitted discharge, conversion losses and load.
Usable energy also depends on chemistry, permitted discharge, conversion losses and load.
See why this fitsPlanning examples and comparison checks
Use the row closest to your situation. The explanation below shows what can move the result.
Comparison table
| Label | Nominal calculation | Energy |
|---|---|---|
| 12 V · 100 Ah | 12 × 100 | 1,200 Wh |
| 24 V · 100 Ah | 24 × 100 | 2,400 Wh |
Planning estimate only. Real runtime varies with temperature, load behavior, battery condition and conversion path.
Use your own watts, hours and reserve.
A realistic input gives you a useful range instead of a false promise.
Open Power Planner →What does this mean
for your choice?
Convert the battery rating
Nominal Wh equals battery volts multiplied by amp-hours. A 12 V, 100 Ah label describes 1,200 Wh nominal. It does not promise 1,200 Wh at the sockets. Use the manufacturer discharge limits for the exact chemistry; do not borrow a lithium discharge assumption for a lead-acid bank.
Work backwards from your appliances
A 100 W average load for eight hours needs 800 Wh at the load. With example assumptions of 85% efficiency and 80% usable battery energy, the nominal target is 800 ÷ 0.85 ÷ 0.8, about 1,177 Wh. Replace both percentages with documented limits; high current, age and temperature can reduce practical runtime.
Keep voltage and charging compatible
A 12 V battery is not a replacement for a 24 V or 48 V bank. Check inverter DC input, charging profile, permitted battery chemistry, battery-management limits and cable protection. Fixed battery systems need an installer qualified for the actual installation. This calculator is not a wiring design.
Check continuous and starting output
Inverter kVA and battery Ah answer different questions. Confirm continuous watts, power factor conditions, starting surge duration and the battery current limit. A protective shutdown can happen before the battery energy is exhausted.
Check the complete power path.
A large enough battery can still be the wrong setup when its output, cable or regional version does not match.
- Measured load and simultaneous output
- Battery energy and usable reserve
- Exact voltage, frequency and complete cable path
- Dated model, package, warranty and seller evidence
Practical answers
Is this a recommendation to buy a locally available model?
No. The calculations and source-region catalogues help define the requirement. Exact Nigerian variants, stock, delivery and approved purchase links have separate checks.
Evidence and sources1 official sourceShow sources
Separate documented specifications from calculated matches.
Products shows source-region technical references. No Nigerian model has yet passed the exact-variant and photograph checks for calculated recommendations. A calculated match is not a compatibility guarantee or a purchase recommendation. Enter your actual device load and check its connections and instructions.