The battery pack that came with the camcorder is VW-VBG070A (see page 9).
There are three higher capacity battery packs (Page 20).
Only the smallest of the three (and obviously the one that came in the box with the camcorder) will fit in the battery compartment - otherwise, the other two larger batteries require an external battery pack holder kit (Page 118 - see the notes associated with the battery line items).
Amazon.com has all three batteries and the external battery pack holder kit - just search the part numbers found in the manual.
I would suggest staying with the Panasonic or Matsushita branded batteries.