Please, please, pleaase..., do not get loose cells on eBay! That is rule number one of running NiMh or NiCd packs. I have found that cells sold on eBay are generally marked as high Mah and when you recieve them they arent anywhere near that rating. I have tested this theory multiple times, I bought some 5500Mah cells and when I charged them up after painstakingly soldering them together with copper bars they only charged to 2346mah approx. I thought no biggie they need to be run and broken in, 6 cycles later and they only increased to 3169mah. Unfortunately most cells from eBay are recycled cells that have been relabeled and they aren't from the same batch meaning they all have a different discharge rate, making a bottleneck. These cells are more than fine for things like around the house devices and toys but unfortunately RC cars have too much draw and requirement for them. I however only race and bash using NiMh and NiCd and I found that NiMh are superior to NiCd and that they don't have a memory effect (you can run for 5 mins then recharge with no downside as long as the batteries aren't hot).
These cells kick some serious ass... (replace (dot) with .)
cheapbatterypacks(dot)com/product/2/Elite-5000-SC(dot)aspx
I have used these and they are great. Happy Bashing