A battery tender may only hold a battery at the charge it has when you hook it up. The battery needs to be fully charged before having a tender put on it.
I have always pulled the battery out of the trailer when it's not in use. I charge it with a auto charger for three days before we go, use solar while we are out and then make sure it is charged after for three days. Once a month I put the charger on for a day to make sure it stays up.
We did do a 16 day trip with electric where the converter tried to cook the poor thing. We also used the converter the next year with the generator for a few hours a day but it never got it full. The converter was turned off when we got solar.
Even with all of the boondocking and the fridge, inverter, solar and A/C testing, our Interstate Grp 27 is 4 years old and is still going strong.
