Moving the battery to the rear will increase steering. Read up on weight placement using a good book like Race Car Vehicle Dynamics by Milliken & Milliken. Also this is a typical practice to increase turn in in sprint car ovals.
I'll try to explain....
Adding weight to the rear will adjust the CG more towards the rear, correct?
So first consider a truck with a perfect weight balance. The CG is perfectly centered so that the weight on all four tires are identical. Tires are identical, foams, springs and shock oils are all identical. This can easily be seen as a truck that neither over steers, or under steers. It is mostly neutral. So before you break traction, pretty much where you point your front wheels is where the truck will go.
Now before I try to explain how a rearward CG biased truck can turn better, I first have to explain how a frontward biased CG truck will turn less.
Lets say that we placed enough weight in the front of the truck that the CG is now located about 2/3rds in front of the rear tires, so 1/3rd away from the front tires. Now the front tires are carrying double the load of the rear. The front tires now have to accept twice the side forces while turning (*look on bottom). This means that the front tires will now slip sooner and require a greater slip angle to achieve the desired heading. The truck now requires a greater steering angle at the front wheels to get the same turning radius as the neutral steering truck. The truck is pushing.
Now lets say we placed enough weight in the rear of the truck so that the CG is now located 1/3rd in front of the rear tires, or 2/3rd away from the front. The rear tires are now carrying twice the load of the front. In a turn, the rear has to accept twice the side forces. The slip angle at the rear will now increase faster and it will reach the end of its peak traction forces sooner. The truck oversteers because during a turn, the rear breaks traction sooner. Therefore this truck requires a lesser steering angle at the front tires to get the same turning radius as the neutral steering truck
(*) This point can be further exaggerated by considering how the side forces on the tires work. Lets say a truck tire is pushed into the ground at about 1 pound. In addition, 1 pound of side force is applied to the tire. It might not slide but it will deform a bit. However, if you push on both the bottom and the side at about 2 pounds or more, it will begin sliding at a critical point that marks the end of the traction circle.