Often batteries that are not "exercised" (used) periodically will go flat by themselves.
There have been reports of the Becker radio causing a drain.

I am going to have to complete that Automotive Electrical Troubleshooting 101 article that's been kicking around in my head for a while.

Some people get one of those book sized solar panel battery chargers around here to keep up the batteries in their RV's. I think I saw one for $19.95 somewhere a while ago.

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Remember, it's not just a car. It's an Adventure.