We had a 2000 watt inverter and Onan Generator installed after market. The installer added a second breaker box and breakers. Most of the outlets and maybe the microwave (can't remember) were redirected from the main breaker box to the auxillary box.
A few of the outlets were not "redirected" to the new breaker box.
It did not carry much of a load for any length of time. Further investigation showed that the wire used from inverter to batteries was not the proper size. The installer cut corners by installing the wrong size wire (#6) . . . it wasn't heavy enough. The manuals specify that "00" size wire should to be used, but he either didn't read the manual or didn't think we'd notice!