King Arms 11.1v 15c lipo (make sure you know what a lipo can do and how to properly use it with charger and gun) will fit in the buffer tube, if you don't want a lipo you can get a nun chuck style batt like a 9.6v i like intellect batt's and they fit as well
as for charger, i personally use a Imax B6 which is a charger that will charge all diff kind of batt's and has a lipo balancer. Airsoft parts has this one just has a different name
http://www.airsoftparts.ca/store2/in...oducts_id=1302