if it is an older champion battery pack you 'might' be able to use lead acid batteries but most of the ones i see now use the AGM or GEL batteries because they are mounted on thier sides. They have to be sealed so they will not leak because of the way they are mounted.

You can find these batteries alot cheaper from 3rd party battery companies. Buying them from champion or a dealer is just nuts unless you like paying twice over what you can get them for elsewhere ;o)