High cell count, when to add a receiver pack?

[squeeforever]

I would certainly put the 8s in the Rusty. 3S and 4S would be close to 10 or 12 cells. 3S is 11.1 volts nominal or 3.7 volts per cell but when fully charged a 3S pack will be 12.6 volts which is very close to 10 cells. 4S on the other hand is 14.8 volts nominal or 16.8 volts fully charged which is actually closer to 14. Take your pick. I would personally try a 1 3s and 1 4s to see what it does.