for anyone else reading this, if you don't have that kind of a connector but want to hook 2 batteries together, the easiest way is to make a connector or buy one. castle makes parallel or series connectors.
I bought one just because it's the same price as buying all the separate materials. and i didn't have to solder it all up.
it uses deans connectors and 10awg castle wire

http://www.castlecreations.com/produ...s_harness.html

also keep in mind when you do this type of thing both batteries have to be the EXACT SAME. type, voltage, mah, C, and manufacture.