I've seen people reference the fact that nimhs only have about 1.2 volts per cell versus 1.5. While this may be true on paper, I find that most charged nimh packs show a good 2 to 4 volts higher than specified. While I'm sure this peak voltage doesn't last long, many devices are designed to operate in a somewhat wide window of voltage levels. Another hobby of mine is metal detecting. The top of the line machine I was using (Explorer II) used 8 AAs. This thing was very power hungry and would eat up a pack of AAs in 4 to 6 hours. With the Engergizer 2500ma nimh AAs I'd get a good 2 to 4 hours longer run time. One tip for anybody thinking of using AA nimhs...These batteries should be charged at a low rate to keep them in top condition and also to give the pack longer run times. I normaly charge my 2500s at .3 amps on my Pirahna Digital Peak Charger. I simply picked up an 8 AA holder from Radio Shack, snapped a 9V battery plug onto it's top, and then hitched the two leads from it to my charger. It takes an overnight charge to charge them. I'd stay away from those quick chargers that Walmart and others sell that wll charge batteries in 30 minutes to a few hours. While it'll work, you won't get full life out of the batteries or run times as long as they should be.