Battery Cross Reference Info

[watersteps]

Hello All, I'm back asking more questions and yes I'm a newbie. I have several RC heli's that I purchased to work on, build and at some time fly. But that will come in time right now I'm still crashing the heli's on my sim. OK first question, I bought a Walkera 60 to start flying with. I want to purchase another battery so I could try to fly a little longer then the one battery will allow. The Walkera has a 12 volt battery with green shrink wrap on it. I cannot find another one just like it to purchase in the USA. Can I get another brand with a little more power and use the same charger? Also I have a used spare battery I got with one of my heli purchases just like the Walkera battery but someone cut the connector off of the 3 wires that go into the battery. Where can I find another connector, the one on the new Walkera is black and has 1 black and 2 red wires. One more question, why does the charger connector only have 2 wires and the battery connector has 3 wires?
Thanks for any info in advance.