Two numbers, in order
Every answer here comes from the same two figures, and people routinely check only the second.
1. Starting watts. A compressor draws several times its running wattage for a fraction of a second. If that exceeds your station's surge rating, nothing happens at all — the inverter protects itself and shuts off.
2. Running watts. Once it is running, this decides how fast your capacity disappears. Air conditioning is a heat-moving load, which puts it among the largest continuous draws in any house.
| Unit | Running watts | Starting watts | From a 2,000Wh battery |
|---|
| Window AC, 5,000 BTU | 450-600 | 900-1,200 | ~3 hours |
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| Window AC, 10,000 BTU | 900-1,200 | 1,800-2,400 | ~1.5 hours |
|---|
| RV roof AC, 13,500 BTU | 1,200-1,700 | 3,000-3,500 | ~1 hour, if it starts at all |
|---|
| Central AC, 2 ton | 2,000-2,500 | 3,500-4,500 | Under an hour — not viable |
|---|
| Central AC, 3 ton | 3,000-3,500 | 5,000-6,000 | Not viable |
|---|
Wattage figures are Champion Power Equipment's published ranges. Runtimes are calculated from the midpoint of each running range with this site's stated 85% inverter efficiency, listed on the methodology page. They are arithmetic, not measurements — a hot day and a poorly insulated room both make them worse.
So: which ones actually work
A 5,000 BTU window unit — yes, for a few hours. A 2,000Wh station with 2,000W or more of inverter starts it and runs it for roughly three hours. That is enough to make one bedroom sleepable, which is a genuinely useful thing during a summer outage.
A 10,000 BTU window unit — marginally. The 1,800-2,400W surge is at or above what most 2kWh stations offer, and about ninety minutes of runtime is not much return for the money.
An RV roof unit — no, without help. 3,000-3,500 starting watts exceeds every portable battery inverter in this class. A soft starter can bring the surge inside range; the one-hour runtime remains.
Central air — no. Not at any portable battery size that exists. This is a standby generator question.
Inverter air conditioners change the arithmetic
Worth knowing because it is the one place the answer is getting better.
A conventional air conditioner runs its compressor at full speed and cycles it on and off. An inverter-driven unit varies compressor speed, so it starts gently — much lower surge — and then settles to a partial load rather than full output once the room is at temperature.
Both effects favor battery use: less surge to clear, and a lower average draw than the nameplate suggests. If you are buying an air conditioner and expect to run it on backup power, this is the specification worth paying for.
How to make a battery last longer on cooling
- Cool one small room, not the house. Close the door, close the blinds, and treat it as a refuge rather than climate control.
- Pre-cool while the grid is up. If a shutoff is forecast, drop the room several degrees first. Thermal mass is free storage.
- Run it in blocks. Thirty minutes on, thirty off, holds a closed room far longer than continuous running and roughly halves the consumption.
- Use fans for people and the AC for the room. A 20-40W fan makes a warm room tolerable for a fraction of the energy. This is the single highest-value substitution on the list.
- Add solar. Cooling demand peaks when the sun is strongest, which is the one load where solar and demand line up naturally.
- Fit a soft starter if the problem is starting rather than runtime.
The arrangement that actually works
For a hot-climate outage lasting more than a few hours, the answer is not a bigger battery. It is a generator outside carrying the air conditioner in blocks during the day, and a battery indoors covering fans, the fridge, and everything else silently overnight.
That uses a fraction of the fuel of continuous generator running, keeps the engine off at night, and puts each piece of equipment on the job it is actually good at. Generator versus power station makes the general case, and the RV page covers the roof-unit version of the same problem.
