My machine runs on 8 AA's, I use rechargeables from Energizer. Got the chrager and 20 batteries for less than 40 bucks. 8 in the machine, 8 back-ups in the Camelbak, 2 in my GPS, and 2 in the digital camera. The chrager will charge 4 at a time in 15 minutes. I had a BADDDD experience with Duracell a couple months ago. Bought 2 packs of eight, put 8 in the machine, and 8 in the Camelbak. Got to the hunting area, turned the machine on... dead. Said a few explicitives, put the other 8 new batteries in... dead. Hiked the hour back to the truck and drove the half hour home.