Personally I would think Gunrunnerjohn's your last battery could replace the 9v. I saw these on the Halloween car. The battery really doesn't fit well. I suspect unlike Sean most folks will try to put the battery in through the door. It doesn't fit that way. At the LHS we demo'd one and just set the battery in on the floor to the side of the clip. FWIW the instructions show the battery clip at an angle which if it was would work.
The wires are really short on this one so the battery has to go horizontally in the clip, but it does fit if centered exactly. The shell comes off super easy. It’s not a big deal. Just thought it would have been nice to have track power for the price, just because sometimes cars sit for long time and should take out battery in case it leaks. But it’s fine.