ORIGINAL: Campgems
I've got two 9cap's and my stock battery and the replacement nicad would not hold up well. I found some NI-MH packs on ebay and I am very happy with them. What I like best is that I can leave them in the car for a couple weeks and they still have a full charge. I think I was killing the Nicads with topping them off before every flying day.
I'd be very wary of flying a NiMH pack which had been sitting for a couple of weeks. The battery experts claim NiMH have a higher internal resistance than NiCD and lose as much as 10% of their charge each day.
That said, I bought a new 9CAPs system last Christmas and upgraded to a 1850mAh NiMH pack in the TX and RX.