House battery question

Most batteries will self-discharge over a month or two just sitting, disconnected. They may read over 12 volts on a voltmeter with no loads but won't have much oomph. Using a "Battery Minder" brand smart trickle charger will keep batteries charged but not overcharged. The BM has a pulsed rejuvenation feature that removes sulphation of the plates and can restore a tired battery to 80 percent capacity. All batteries are not created alike, and they may vary with use and abuse. Keeping connections clean, checking state of charge, and keeping electrolyte levels above the plates is just part of RV'ing.