I measured balance with tips like those available from hudy
you want your car to be heavier up front not in the rear ...
this is why with 5cell, everybody runs the battery forward ...
pushing the weight further outward messes up the handling of the car quite a bit this is why I didn't put the lead to the side of the lipo but under the lipo to get the same weight distribution the car was originally designed for
for ETS races the weight limit is 1350 so I only have to add about 50g as the tires are super heavy
I use a GM 40C pack (#98989) which features cell bumps
I just filled up all the space left with lead but if you don't need all the weight make sure it's as far forward as possible