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. Look at Ebay item 270193458881. I bougt two, not four, but the price is right and the shipping is quick. The only down side was that the end is a universal end and it won't fit the 9CAP socket. I cut the cable off a couple scrap batteries I had and soldered them to the leads from these batteries and it works well. I first though of going to a Li-po replacement, but the cost of extra chargers, as well as the cost of the battries nixed that idea.

Don

PS, I have no intrest in the seller above other than having purchased two of the packs and liking them. Your mileage may vary.