Batteries will make a lot of difference in the enjoyment you get out of your Pede. The upgrades available for these things can really tear into your checkbook though. Not much is really "needed" though.
One thing that will save you some cash though is a RPM front bumper.
The upgrades I have done to my son's Pede are
RPM front bumper
extended front arms (Losi LXT)
Nitro Rustler front spindle set up
Nitro Rustler rear bearing carriers
RMP Talonz (made for Nitro Traxxas 2.2 vehicles)
Masher 2000 tires
Sermos added when I bought new Batteries. Cheaper and more finger friendly for the kid than deans
15x2 Endurance Racing Products (ERP) motor (I think they are out of business now but this motor was new in '94 and only run in one race before put in storage)
Big Bore shocks
e-clip capture suspension pins and SRT tie bar. This is a great mod and no more messing with those screw type pins and stronger front bulkhead.
There might be more that I have forgotten
Here is the most recent picture I have. I think all I added after this pic is the SRT Tie bar, Big Bores, and Sermos