I was in the process of replying to one post about batteries when I realized that there often are questions related to batteries in this forum. I know.. there is a separate section for batteries, but questions often appear here, in the Beginners forum.
So, I thought I might add something to this discussion by offering a few suggestions of my own.
I have, in the past, used Radical RC as my battery source. Dave Thacker, the owner, has a great reputation and can be relied upon for a straight answer to questions regarding batteries. And, he has the background and education to back that up.
So, below are a few links to his FAQ section and other sections on batteries that may help you decide on what kind of battery to use and how to charge them.
Battery FAQ's:
http://members.aol.com/davthacker/abattfaq.html
NiMH issues:
http://members.aol.com/davthacker/nimhfaq.htm
4.8 volts or 6 volts for the RX pack:
http://members.aol.com/davthacker/4or5cellsfaq.htm
Soldering your own packs:
http://members.aol.com/davthacker/cellsoldering.htm
I hope this helps.
DS.