I do not plug our Monty into shore power for storage. I use a Battery Tender Plus and have not had a problem in 8 years. They keep the battery charged but does not overcharge like a regular battery charged can do. They are available at Walmart or parts store and have a light system so a quick glance lets you know what is going on.
Francis and Linda
2016 3582 RL
2009 Freightliner M2106 Cummins 8.3
I have 2 group 27 batteries. A REAL battery disconnect was installed. Batteries have held a charge for 3 months when disconnected. It would be easier to take the generator and charger to them if they go down more than 20%.