The best that will fit w/o any modification?
If you want a 2cell w/o any modifications the maxamps.com 2s2p 6000mah
If you want a 2cell and will use a velcro strap as hold down, the 12000mah 2s4p pack is amazing
If you want that 60-70mph range you will need a 3cell
maxamps has a 3s 5000mah pack that fits in the stock location
if you dont mind doing the velcro mod the 3s2p 8000mah is the absolute best battery you can snag for the VXL
. Huge speed 70+ and sick run times. It is actually fast enough that you can run in training mode 50% if you want to have a bit more control and bash or race