Short answer: size by running watts for everything on at once plus the starting surge of your biggest motor (usually the AC). Most 13,500 BTU AC setups need about 3,000+ running watts, or a smaller unit plus a soft start; check the AC's specs.
| If you need… | Look for |
|---|---|
| Charging batteries, fans, laptop | ~2,000 W class inverter generator |
| One 13,500 BTU AC | ~3,000–3,500 W class, or 2,200–2,500 W with a soft start (test first) |
| 30A RV, AC + microwave | ~3,500–4,500 W with a TT-30R outlet |
| Two small units | Parallel kit doubles output but adds weight |
| Propane on board | Dual-fuel units run on LP; output is usually lower on propane |
Running watts must cover everything on at once; starting watts must cover the biggest motor's surge plus the rest. Generators lose output at altitude (often cited around 3–4% per 1,000 ft; see your manual). For full detail use the RV generator size calculator, or compare against a power station.
Safety: These are general estimates, not a design. Follow your equipment manufacturer's instructions and local electrical code, and consult a qualified electrician for anything connected to shore power, a house, or high-current batteries.
Add the running watts of everything you run at the same time and make sure the generator's rated watts cover it, and that its starting watts cover your AC's surge.
Sometimes a small AC can start on a 2,000–2,500 W inverter generator with a soft start, but results vary with the unit, heat and altitude. Many owners use about 3,000 W or more.
They are usually quieter and produce cleaner power for electronics than open-frame generators, and many campgrounds have noise limits.
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