Originally Posted by Still Kickin
Make it easy on yourself, buy one of these cigarette lighter battery tester | eBay
. Then look up the 12v battery chart so you can determine % left. It's important to calibrate the reading on your tester, so you can make any adjustments to the chart data.
This is the easiest for most Small RV's, The panel mounted meter is very nice option if you want to have one mounted and constant view, using a voltmeter you either have to get to the battery or use a test points in a cigarette power port.
Just remember not let your battery get below 50% power or 12.2 volts for max life of you battery.