A/C, fridge, and battery charger will just about max out a 20 amp circuit. Do not try to run the water heater on 110, microwave, vaccuum sweeper, etc. while the A/C is on and you should be fine.
And DO use the ETI provided power cord not a "normal" extension cord.
Doug and Karen
2014 Escape 19'
2005 Toyota Tundra V8 Access Cab