If you rely on others for answers, from what I read the Rustler has what two types of battery choices and you must what set up for the battery you want?
Since I don't deal with the other battery you can add a 3S higher Currant and larger cap for what you want, speed as well the speed gear... read the info in the manual at traxxas
https://traxxas.com/products/models/...-vxl?t=support
off road thread is where rustler threads are or jsu tthis site went down hill.