I once made the mistake of turning on a 12-volt hair-style-dryer-type dew zapper from the same battery as the 10-inch LX-200 GPS. Autostar lost its alignment and slewed to some random spot; I had to start over.
Sam's seems to carry a new 12-volt jump start battery every month or two, with prices ranging from the $40s to the $80s, and with various other features (e.g. built in air pump, AC inverter, or whatever).