[E-Revonut]

You will not get beeter balance out of dual packs, the motor and batteries come close to balancing each other out. Go to Hobbyking.com and get a Turnigy battery to stay in your budget. RC-Monster store also has some awesome batteries but they come with a bigger price tag. The Turnigy batteries will do just fine for you, 4s 5000mah would be a good battery. RC-Monster has some great battery trays so I would suggest ordering one with your motor mount, don't forget pinion gears, without doing the math I would guess about a 15T would be a good start, at least for the track.