[Alan Roehrich]

Actually Chad, a battery sitting on concrete that goes through considerable temperature changes will discharge because water condensation on the battery allows current to flow across the battery. Any water that is not perfectly free of all purities will conduct electricity, and water that condenses on a battery isn't pure. It does not always happen, but in climates where the temperature changes 20-30 degrees in a day or so, it can happen.

Beware of battery tenders and trickle chargers. I strongly suggest they not be left on batteries that will be unattended for any real length of time. While it is very rare, there have been instances of various factors causing even very low current chargers shorting out and causing fires. You'll be much safer if you just connect a charger set on 2 to 10 amps and charge your batteries for a few hours once or twice a month or so while you're around, and that will be enough of a regular charge to maintain battery life at acceptable levels. Charge your batteries while you'll be around where ever the batteries are, maybe throw the charger on when you get home for the weekend and can look in every so often, and take it off before you call it quits Sunday evening. It could prevent a tragic and catastrophic loss.