You're not going to get a definitive answer because this has been discussed at length and people dissagree.
On a car like the L4, which was not designed for brushless motors, you should balance the chassis by itself. The reason is that the BL motor makes the motor box heavy on the left (non-gear) side. So if you balance the whole car you will add extra weight to the right side of the chassis to compensate. But with tires on the car and it sitting on the track that extra weight is pushing down on the right front tire more than the left. The motor pod does not come in to play because it sits level on the rear axle. I believe the disagreement may come from the fact that it makes little difference which way you do it as long as the car is not hugely out of balance.
What does make some difference is that you will have to add a lot of weight to the electronics side of the car to compensate for the battery, and the car will be quite overweight. Most of the cars these days can weigh in around the minimum so that can be a disadvantage. Like Lonny said, you should just get the excellent Speedzone 1s saddle pack. It will fit with little to no modifications and you'll have no balance issues (from the battery at least)
