If you disconnect a battery so those parasitic devices can't draw power from it, the battery can be left for at least a month without charging.
Batteries need charging when their voltage falls below 12.5 after several hours without charging. (Charging causes a temporary higher voltage that makes it impossible to read the state of charge with a voltmeter.) This is confusing when charging. The charger or alternator will run the voltage up over 12.6 in a minute but it probably needs at least an hour to provide a lasting charge. You will need to read the voltage frequently to get the experience to be confident your battery is charged and will remain charged for a month while disconnected.
A "smart charger" is supposed to feed current into a battery until it senses the battery is fully charged but my charger isn't all that smart in cold weather.
I think a battery monitor is great for the house batteries. It counts the amp hours (energy) going into and out of the battery bank displaying the per cent of full charge all the time. The Trimetric battery monitor is the top of the line but my $20 Chinese one works very well.
eBay battery monitor
