Can I leave my T/C plugged in to A/C when not in use?

I keep the camper plugged into AC always when it's at home, but the AC line is on a timer (same one I use for the Christmas lights on the house) so the AC circuit is only on about 6 hours per night. My theory is this charges the battery only a few hours a night even though the onboard battery charger is a good one.

I've been doing this for years and the Costco el-cheapo camper battery usually lasts 5 - 6 years between replacements.

-Joe