Ponytail Mom, note that the voltmeter method of measuring the state of charge only works 8 hours or more after charging has been stopped. While charging, the meter just measures the charging voltage. When the charging is stopped, the voltage on the battery takes hours to fall to a stable value as the chemical reactions in the battery finish. Fully charged = 12.6 volts, 12.0 is as low as you go without damage.
Starting a vehicle with a dead battery by charging it will take a few hours. Would connecting the booster cables while the engines are stopped help? Might there be a way to eliminate the transient currents - perhaps a coil in the booster cable wire? Or a big capacitor across the target battery?
Current drawn by RV fridge on propane - this source says a quarter of an amp or 6 amp hours per day unless equipped with auto defrost. Much less than that for the detectors I think. One battery should last a week.
http://www.rvnetwork.com/index.php?showtopic=103161
This has been my experience, too.
