You know, the 10 ton 32" at the observatory uses only 0.3 amp at 12VDC when tracking. The one consideration I did not see you mention is the effect of cold temperature on battery life. One of our club members used re-chargable battery packs. He would swap when a pack ran low during the night. His problem was that his son kept running down the batteries in the afternoon playing with his remote control model cars!