Having a camper with an electric stove and no genset, I tend to obsess a bit about this stuff.
Two comments:
-- When should I charge? Whenever you can and as fast as you can. Lead Acid batteries do not like to be discharged and leaving them discharged is an easy way to convert them into paper weights.
-- A volt meter is interesting, but very limited. When on charge, it tells you the voltage of your charge source, not your battery. And the rest of the time, it gives an artificially low reading as most RV's are discharging all the time. Your refrigerator is probably you biggest load.
A hour counter, such as those made by Bogart, Victron, or Xantrex is a really, really useful investment, even with all of their failings. Otherwise it is as if you are trying to determine how much fuel you have left by looking at the speedometer.
