Join Date: Jul 2008
Location: Austin, TX
Bikes: Giant OCR2, Bridgestone RB-T, Bike-E, Vision R-40, Novara Safari
It could just be the battery in the 305, which you could probably replace yourself if you're so inclined, but if not, Garmin probably won't charge you very much (not compared to the cost of a new unit, anyways) to replace it.
Actually, even if it's totally trashed, they'll probably fix it for a good deal less than the price of a new unit. Certainly, give them a call.