Okay, so I just ran my first two summer camps with the Lego NXT and the Lego supplied rechargable battery pack and DC power supply. In the first camp which was a half-day version for six weeks. The teams only had to recharge the battery pack every couple of days as they only were in robotics for 1 to 2 hours a day. I don't have any good data for the full-day , two-week camp as I only taught the morning and witnessed the teams recharging over-night for good measure. Lego must have designed the NXT to operate on the voltage coming from these packs and I haven't a clue as to what type of system they are using, NiCad, LMH, Alkaline ,,,
