On my 50s I run two nimh 2000mah and a 2000mah on the ignition. But I'm now just getting into the A123s.
You guys want A123s Get them from booma-rc. his service is unbelievable. Here is a link.
http://www.booma-rc.com/default.aspx...Code=BRC-38207
I'm now building an Aeroworks 100cc extra 300. I'll be running two 2700 A123s into a power safe JR r922 power buss receiver. And a 2000mah Nimh on the ignition.