hey matt, i use to have the same problem with alot of stuff i was storing, but i bought 2 trickle chargers that is simular to the one i put in the link. i put one on my golf cart and one one my car in the winter and swap it with my lawn mower and other stuff just to give um a zap ever now and then, if your storing in a cold area that itself can kill a batterys life, i seem to be getting more life outta my batterys now using the chargers....hope this helps ya..
http://cgi.ebay.com/12-Volt-Battery-...ayphotohosting