Add the running watts of everything that will be on together, then add the extra startup watts of the single biggest motor. A 13,500 BTU RV AC typically needs a 3,000–3,500 W generator (around 2,200 W with a soft-start kit on many units). A 50-amp RV running two ACs usually needs 5,500 W or more. Generator output drops roughly 3.5% per 1,000 ft of elevation.
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.
Usually 3,000–3,500 starting watts for one 13,500 BTU AC plus small loads; a soft start often lets a 2,200–2,500 W inverter generator work. Check the AC's specs.
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