Just plug it in. Use your shore power charger and let it charge the batteries. This is the way a built in genset works in nearly every RV. Some chargers work less efficiently on genset power (will not produce rated output) but on the Honda inverted power it should work fine. A 50 amp charger will only use about a third of the power of the genset, so the rest is available.
One thing though, please don't assume (as many seem to do) that that Honda is "so quiet you can't hear it". There is nothing like driving well off the beaten track into the wilderness, only to listen to the constant drone of a genset.
