Pro Amps do a 4000 Lipo and LRP do a 4600 which all fit in the MO5 and MO3. Depends on how much you want to spend on batteries and whether you prefer deans plugs, corally plugs or the standard tamiya plugs. Most replace the Tamiya plugs with a Deans. The 3800 IP is a good battery also. With the corally plugs just make sure you do not reverse polarity them or else your ESC will let out the smoke quickly.
Later,
50 Cal