not sure what you mean by 'generator battery'....
do you mean you have a difficult time 'starting' the generator?
if so, it is cranked from the HOUSE Battery bank, the same batteries that run your 12v lights, fans, furnace, water pump, etc., and the same battery bank that provides the power to and thru the INVERTER to power 120v outlets, like the fridge, microwave, and all outlets when not running the Generator and when not plugged into Shore Power.
A 100w solar panel will collect about 5amps on a bright, good sun day, for several hours, and can help aid in keeping the HOUSE batteries charged, but probably will not, by itself, keep the batteries charged at a high level IF you are using the coach and the 12v devices and the Inverter, the fridge, etc. The use of the generator will be required to recharge the HOUSE battery bank, maybe several times a day, to maintain that charge while you are using the coach, when you are not plugged in.
also, setting up your AGS thru the Magnum remote panel to AUTOMATICALLY start your Generator when the House Battery banks needs charging is a great tool, and makes life much more convenient when letting the generator maintain the battery levels.
two Campers, two Electric cars
former diesel pusher traveler