Extending battery leads
If you feel comfortable with your soldering skills, go ahead and splice in the lenght that you need. Be sure and use heat shrink tubing and stagger your splices so you do not have a big clump of splices at one point. Sounds as if you have a basic setup with standard servos, so I doubt you would need the heavier wire, but this depends on the distance you are placing the battery.
Vince