I wouldn't even bother with ni-cd's but as far mah go's it will only tell you how long it will run for not really a incraese in any power but i wouldn't get any thing less than 3000 mah packs because the run times at any less aren't worth it! [trust me] but an increase in voltage will give you more power guaranteed! and only use peak chargers for ni-mh/ni-cd that way you get a full charge every time with out going over, plus a lcd srceen on it is always a good thing! so you can see how much your batterys take in, also rule of thum is charge at no more than the rate of mah like if it's a 3600, then charge it no more then at 3.6A or if it's 4000 then no more then 4.0A that way your batterys last there full life!

p.s. I got two reedy 3600 8.4v packs for sale on e-bay right now for $40 shipped!http://cgi.ebay.com/ws/eBayISAPI.dll...fvi%3D1&_rdc=1