How to mount 12 or 14 cells in stock revo?

[BrianG]

That's good to hear, but I suspected as much. Even though the batteries are heavier, they sit closer to the center line of the chassis, which helps offset the relatively lighter motor, but that sits more outside the center line.

IIRC, you are using a 14 cell "brick" right? If so, a 4s1p Maxamps 10Ah pack is just about a perfect replacement size-wise if mounted on edge. The pack will be a bit taller (59x158x42) than the 14 cell brick (46x161x44), but the length and width are just about perfect. And the weight (813g) is very close to the same as 14 cells (910g). A 5s pack will be about 10mm wider and 100g heavier, but the voltage and runtime would be well worth it IMO.