Best option is to wire the ESC with two connectors like what you see on the Traxxas eRevo and eMaxx as an example.

If you have inboard 2S packs you can do what I did and just put the bullets on your ESC and make a jumper wire with the bullets on it to bridge them in series (you do not want parallel wiring btw to make a dual 2S into 4S power). Thing with bullets though is you have to wire them at a 90 degree angle to the bullet to fit the tray in most cases for 1:8.

Nice thing about inboards and bullet connectors is that you are in total control of the amount of extra wire flopping around in the chassis.