Battery losing charge

Unless specified differently, the industry standard current draw is 35 milliamps, (.035 amps) for all of the silly computer memories. At that rate a good battery is expected to start the engine after sitting for up to three weeks. Some manufacturers specify 50 milliamps because they've added even more unnecessary computers to incorporate all the toys and gimmicks people demand on their cars.

What you might consider is installing a solar charging panel that plugs into the cigarette lighter socket, but that will only work if you do not have to turn on the ignition switch for the lighter to work. If you do, look for a charger that connects directly to he battery.