RE: 12 volt charge?
It's a good idea to keep 12V batteries fully charged. You might want to consider investing in a "float charger" or "battery maintenance system" for your battery, as it's a Ron Popeil set-it-and-forget-it type of thing. You plug it in, connect it to your battery, and leave it. When you want to go flying, just unplug the charger and head out the door.
If you have a Harbor Freight in your area, they have a float charger on sale from time to time for less than $10. Most auto stores now sell float chargers for maintaining the batteries on classic/collector cars.
For heavy flying days, you would want to charge it at the end of the day.