Wow, what a trade up!

The battery boxes are located on each side of the transmission, under the operator's platform. On each side there is an outside steel cover plate that is held on with two bolts that go in from the bottom. Take them out and the plate will slide down and off, and the batteries will be there. If it is original, there should be a pair of 6 volts on each side. Most guys have switched them to a single 12 volt on each side.

An easy way to charge the batteries is to hook your battery charger to the same post that the heavy battery cables go to on the starter, being careful not to cross to any other posts. This will be your positive post, the other end of each cable goes directly to the positive post on each battery. Hook your negative to the frame, or one of the starter mounting bolts, and turn on the charger.