Go to Home Depot or Lowes. In the electrical dept they should have a roll of # 6 or #8 wire that is a black and red. Same as tour motor is wired with. Get 2 8 ft sections. Take plug off each one. Splice the new wire to old wire preferably by soldering them together. If not get proper size wire crimp on connectors. Someone in electrical dept should be able to help. Then install plug or ring eyes on other end to connect to battery. If your motors already have ring eyes or clamps you can skip that part. Size 8 if that's what they have is plenty big for the motors you have.
Proud Member of Team Geezer
Charlie Weaver USN/ENC 1965-1979