Whether the inverter can power your brother's microwave is one matter, the toll to 2 batteries for just a few minutes of microwave use will take a significant bite out of the onboard 12 volt reserves. This will eventually lead to powering up the genny earlier and longer to replenish consumed amphours, our inverter could power up our microwave but I always would run the genny since it would literally zap our 2 battery setup.
We have plenty of solar which helps, inevitably when using high amperage items (microwave, blow dryer, curling irons, coffee makers, blenders, etc.) on just a dual battery bank the generator ends up being used more than necessary. We have an Iota IQ4 smart converter that quickly restores our batteries during bulk charging, having a remote start genny (Onan/Champion 3100) makes it easy for us to use high amp items at our convenience.
