I need to have mains connected through the winter to run the dehumidifier but I have fitted a switch to allow the mains to the battery charger to be turned off when I am not onboard and I also turn off the services from the service battery removing the key switch so there is no load on the battery. The battery will maintain it’s charge for many months like that. The battery charger should draw almost no load from the battery.
I also have a NASA BM1 battery monitor so I can see that when I turn on the battery charger it takes only minutes to bring the battery up to full charge.