I believe you could actually use any type of battery that outputs 9V. (Granted, you might want to stay away from something weird and dangerous like this.) As long as it looks like a 9V and says "9V" on the outside, you should be good to go.Are rechargeable 9 volt batteries allowed in the MagLev trial event in Wisc? It doesn't state they are not. Thank you!
(Never a bad idea to bring a couple alkalines as backup.)
Also, mxz55o, you don't have much choice if you're buying a new track, right? The new Pitsco ones don't match specs, so you have to go with the Kelvin ones. They'll most likely use those at nationals, too--unless someone had an old set of Pitscos lying around.