Hi,
Most chargers do not "Turn off" once charged, but instead charge at only about 13.2 to 13.4 volts. That voltage is not high enough to boil out a lot of water from the battery, but also not high enough to quickly charge the batter.
If you are running a generator and spending $4 an hour to run it, then you want the charge to be quickly as possible, even at the cost of needing to add more water to the battery. So 3 stage are better, as when first plugged in will go into the bulk mode and run at around 14.4 - 14.7 volts for an hour or so. When the charge current is less than about 30 amps, normally they drop to about 13.8 volts for a time, then as current drops below about 10 amps, it will go into the "Float" mode - at 13.2 - 13.4 volts and stay there.
My Truecharger will stay at 13.2 volts for weeks, then every 30 days will charge at 14.4 volts for a while, to automatically get rid of any buildups on the plates, without using to much water. The Truecharge also monitors the battery voltage while not plugged in. If it detects less than 11.5 volts, it will start charging at the bulk mode, otherwise will start charging at the absorption mode.
A 4 stage charger will add a "Equalize" mode to the mix. You can manually tell it to "Equalize" and the voltage will to way up, say to 15 volts for a few hours. This will clean up the battery plates and is recommended every 6 months or so. My SB 50 solar charger has a equalize mode, and works great - when done every 3-4 months to keep the batteries in top shape. But I need to add water before and after equalizing, and also remove my hydrocaps, because there is a lot more water loss during equalization.
Would I put a upgraded charger in my next RV? No. I hardly ever use the charger that I have. It is built into my M1512 Trace inverter/charger, with a 70 amp max output at 14.4 volts. The reason I rarely turn it on is that I have a 400 watt solar system, so normally I leave it off to allow the solar to do all the charging.
Exceptions to that rule are when I have used more than 120 amp hours from my battery bank overnight (watching to much Direct TV) and want to make up all the power during the next day. So I can run the generator and max amperage from the charger for about 1 hour, putting back about 40 AH in that time. Most chargers will drop to about 30 amps after a hour, so running the 4 KW generator and only putting in 30 amps X 13 volts (about 390 watts) is not a wonderful way to utilize the generator.
I would only run the generator to recharge if I had plans to stay put another 3-4 days, and wanted full batteries at night. Normally if I plan on driving, I would let the battery stay low, and save the generator fuel (and avoid the noise). If I was going home, then I would plan on not charging at all, and let the solar top off the batteries in the next week or so.
For heating, I use a Olympic Catalytic heater. It heats without any 12 volt power. But is vented inside, so I need to open all 3 roof vents about 1/2" and a window about 3/8". This has never tripped my CO detector in the 20 years it has been in use.
Good luck,
Fred.
