Quick answer
A 1HP inverter aircon usually draws about 300–800 watts, depending on how hard it’s working. On a 48V 100Ah (5.12 kWh) LiFePO4 battery, that’s roughly 5–14 hours, and around 9 hours in a typical bedroom at night. A smaller 12V 100Ah battery gives only about 1.3–3.5 hours.
How much power does a 1HP inverter aircon use?
An inverter aircon doesn’t run at one fixed power. It works hard at first to cool the room, then slows down to hold the temperature:
- Cooling down: about 700–900 W for the first 15–30 minutes.
- Holding temperature: about 300–500 W in a well-sealed room at night.
- Hot afternoon, sunny room: can stay near 700–800 W.
Check your unit’s rated power input (watts) on its sticker or energy label for its maximum.
The formula
Runtime (hours) = Battery kWh × 0.9 (usable) × 0.9 (inverter) ÷ aircon kW
The two 0.9 factors account for not draining the battery completely and for losses in the inverter that turns battery DC into AC for the aircon.
Estimated runtimes
| LiFePO4 battery | Usable energy | At 400 W | At 600 W | At 800 W |
|---|---|---|---|---|
| 12V 100Ah (1.28 kWh) | ~1.0 kWh | ~2.6 h | ~1.7 h | ~1.3 h |
| 12V 200Ah (2.56 kWh) | ~2.1 kWh | ~5.2 h | ~3.5 h | ~2.6 h |
| 24V 100Ah (2.56 kWh) | ~2.1 kWh | ~5.2 h | ~3.5 h | ~2.6 h |
| 48V 100Ah (5.12 kWh) | ~4.1 kWh | ~10.4 h | ~6.9 h | ~5.2 h |
| 48V 200Ah (10.24 kWh) | ~8.3 kWh | ~20.7 h | ~13.8 h | ~10.4 h |
Estimates only. Real runtime depends on the room and weather, and the inverter itself uses some power even when idle.
What makes it last longer (or shorter)
- Set temperature: 25–26°C uses much less than 18–20°C.
- Room size and insulation: close doors, seal gaps, and use curtains on sunny windows.
- Time of day: night runs are much cheaper than hot afternoons.
- Pre-cool on grid or solar before switching to battery, so the battery only has to hold the temperature.
- Add solar: during the day, panels can power the aircon directly and recharge the battery at the same time.
Other things you need
- A pure sine wave inverter of at least 1.5–2 kW for a 1HP unit. Modified sine inverters can damage the aircon’s electronics.
- A higher-voltage battery bank (24V or 48V) is better for aircon loads. At 12V, an 800 W load pulls about 70 A, which needs very thick cables and runs hot.
- Proper wiring and breakers between the battery, inverter, and aircon circuit.
Why LiFePO4 and not lead-acid?
An aircon drains a battery deeply every time. Lead-acid only gives you about half its rated capacity and wears out quickly under that kind of use. LiFePO4 handles it for thousands of cycles. See LiFePO4 vs lead-acid for the full comparison.
Bottom line
For a full night of 1HP inverter aircon on battery, plan for about 5 kWh of LiFePO4 (48V 100Ah) with a 2 kW pure sine inverter. Add solar panels and the same system can recharge by day and cut your electric bill too. See Can Solar Save Me Money?