Point of data for the truck charging. We have a Trimetric monitor installed and with the truck idling we had 4 amps going to the battery. Will take a long time to charge at that rate.
Read this and you will know more about batteries than you ever cared to.
We used to kill our group 27 130 amp hour battery overnight with a bit of furnace use. Charge with the generator the next day and do it again.
Now with properly charged golf cart batteries 220amp hours we might bring the batteries down 15% with heavy furnace usage. 85% is the lowest I have seen on the batteries all season. That is 33amp hours which is something our old group 27 should have easily handled. I don't think it was ever really fully charged to begin with and it was 1 year old as well.
Invest in a battery monitor and know for sure. Best mod we have done to our trailer.