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A Air Cooler draws about 180W, so a 150Ah 12V tubular battery runs one of them for roughly 3 hours 30 minutes on its own. That comes from 630Wh usable energy divided by 180W. Pump plus blower motor; the single heaviest load most Indian inverters are asked to run.
Pump plus blower motor; the single heaviest load most Indian inverters are asked to run. The 180W figure used across this page is a typical mid-range Indian retail unit — check the nameplate on yours and put the real number into the calculator, because a 10W difference on an appliance you run for six hours is 60Wh out of a budget of only a few hundred.
Category: Cooling. People search for this as desert cooler, room cooler, cooler watts — all the same question, and all answered by the same arithmetic.
Usable energy is Ah x 12V x 0.7 efficiency x 0.5 depth of discharge. Divide that by the appliance draw and you have the runtime with nothing else connected.
| Battery | Usable energy | Runtime with one unit | Runtime with two |
|---|---|---|---|
| 100Ah | 420Wh | 2 hours 20 minutes | 1 hour 10 minutes |
| 120Ah | 504Wh | 2 hours 48 minutes | 1 hour 24 minutes |
| 135Ah | 567Wh | 3 hours 9 minutes | 1 hour 35 minutes |
| 150Ah | 630Wh | 3 hours 30 minutes | 1 hour 45 minutes |
| 165Ah | 693Wh | 3 hours 51 minutes | 1 hour 56 minutes |
| 180Ah | 756Wh | 4 hours 12 minutes | 2 hours 6 minutes |
| 200Ah | 840Wh | 4 hours 40 minutes | 2 hours 20 minutes |
| 220Ah | 924Wh | 5 hours 8 minutes | 2 hours 34 minutes |
| 250Ah | 1050Wh | 5 hours 50 minutes | 2 hours 55 minutes |
Nothing stops you connecting more units — the limit is runtime, not the inverter, until you hit the surge ceiling below.
| Quantity | Continuous draw | Runtime | Band |
|---|---|---|---|
| 1 | 180W | 3 hours 30 minutes | Moderate |
| 2 | 360W | 1 hour 45 minutes | High load |
| 3 | 540W | 1 hour 10 minutes | High load |
| 4 | 720W | 53 minutes | High load |
| 5 | 900W | 42 minutes | High load |
| 6 | 1080W | 35 minutes | High load |
Very few appliances run flat out for a full hour. A fridge compressor cycles, a mixer runs in bursts, a pump fills a tank and stops. Battery Buddy asks for minutes run per hour and multiplies the wattage by that fraction — which is why its answers are usually longer, and more honest, than a calculator that assumes continuous draw.
| Minutes run per hour | Average hourly draw | Runtime on a 150Ah battery |
|---|---|---|
| 15 min | 45W | 14 hours |
| 30 min | 90W | 7 hours |
| 40 min | 120W | 5 hours 15 minutes |
| 45 min | 135W | 4 hours 40 minutes |
| 60 min | 180W | 3 hours 30 minutes |
This is a surge-sensitive appliance. Battery Buddy applies a 2x start-up multiplier to a Air Cooler, so one unit spikes to about 360W for a second or two at switch-on. Your inverter has to survive everything else already running plus that spike — not just the average load.
Peak demand = total continuous load + the single largest start-up surge. The sizing advisor runs that check automatically for whatever mix you enter.
These are complete household and shop profiles we model, each with its own worked page.
| Profile | Average draw | Backup on a 150Ah battery |
|---|---|---|
| Air cooler + 2 LED bulbs | 198W | 3 hours 11 minutes |
About 180W while running. Pump plus blower motor; the single heaviest load most Indian inverters are asked to run. Always confirm against the nameplate rating on your own unit before sizing a battery around it.
Roughly 3 hours 30 minutes with nothing else connected: 630Wh usable divided by 180W. Add anything else to the inverter and that time drops proportionally.
Battery Buddy applies a 2x multiplier, so a single unit peaks near 360W at switch-on before settling to 180W. That spike, not the running load, is what trips undersized inverters.
Yes — one unit runs about 2 hours 20 minutes on a 100Ah 12V battery at 70% efficiency. Whether that is enough depends on how long your outages actually last and what else shares the inverter.
The figures assume 70% system efficiency. An older battery, low electrolyte, corroded terminals or thin cabling all reduce the effective factor. Measure yours with the efficiency estimator and re-run the numbers — it takes one discharge test.
Battery Buddy is free, needs no sign-up, sells no batteries and shows every formula it uses. It is built by Flocci Technologies, an India-first AI-native software studio behind 30+ apps that share one Flocci identity.