How long on the shelf? An automotive battery will do kind of the same thing. New off the shelf and installed into a car, say, a newer Sebring (or any newer model for that matter) and left there not running for a month it will go below the point of starting the vehicle. There are micro amp draws from the ECM's memory, whatever else that can add up when the alternator is not run (engine running) in order to recharge it. Could be something like that. Start it up and run for a pic or two and the battery has yawned and stretched and is good to go. Day or two, shouldn't be doing that. Month or more at a time, could explain it I guess.