KG7DKF.. When my Interstate U-2200's were new and I did not camp over winter (Though I do admit to using the rig a bit, IT's where the TS-2000 lives after all) I kept it plugged in full time save for when Detroit Edison failed us and I had to reverse the neutron flow or something like that (Actually the house was properly wired with a generator transfer switch and the motor home wired to feed it)
I watered the batteries every Mothers day, Weather they needed it or not as the saying goes (They could always use it but it took like 14 months to "need" not the 12 between mother's days) Today it's a bit more often but they are getting a bit long in the tooth as i were (going on 9 years).