[Siouxicide]

This may be an amateurish question, but here goes anyhow....

After a trip my Sub sat out overnight and the next day it flat wouldn't start. Thought maybe I ran down the battery somehow, got a jump, and drove the trip back no prob. Sub sat for 2 days, then my wife took it around town. Was slow starting on her last stop but made it home. Very next day we go to take it and again it's too dead to start. Jump it and now I get the warning message listed in my title. Drive it like this and the voltmeter is showing 14-15V so it's not anything but the battery that I can tell. Also, the rig started just fine after sitting in the cold all that night and the message went away.

My question is, is there anything other than the alternator that can affect how the battery is charged? This rig has so many FREDs that I'm worried there might be. I assume it's the battery with a bad cell, but you can't buy aftermarket yet and I assume the dealer will nail me for $200+ for one.