Ditto. For a typicaly 40-60 sized plane, a 600mah pack is fine, be it NiCd or NiMH. There are several reasons for using NiMH, such as lighter weight and the fact that NiCds will be phased out in the next several years due to the toxicity of Cd. NiMH do not offer better capacity, but they can offer more capacity at the same weight of a NiCd. This is because if all else is equal, NiMH cells don't weigh as much as NiCd cells. I think this is where the confusion starts as vendors will make claims like "Our NiMH have more capacity than NiCd." You gotta read between the lines... all they are really saying is if you have two packs at the same weight, the NiMH will have more capacity becasue a large NiMH cell (say 800mah) weights the same as a smaller NiCd cell (say 600mah.) Of course a 800mah pack has more capacity compared to a 600mah pack. As for the weight savings, the diff between NiCd and NiMh on a 600mah pack is probably a ounce or less... not enough to worry about on 99% of planes. Cheers.

How long will they last? Depends on your plane setup and flying style. On a trainer, probably 6 ten minute flights would be safe. But, I'd suggest you get a bettery checker and check your batts before every flight, even if you just charged the battery.