OOH!
What you've got there is the AA Battery Grip for the SF-series. These are pretty rare, as the vast majority of SF-series cameras come with a grip that's made to take the 2CR5 lithium battery (the AA Battery Grip seems only to have been offered as an accessory, and never with the camera). It's a nice find, crack or no.
I would try to patch that crack somehow (though I don't know how to do it). If you didn't mind paying $5-$10 for the lithium battery (they last quite a while,actually) go ahead and buy the parts camera.
Or you could get lucky again and find another AA grip!
To get the grip off you just unscrew it using a coin, just like you would an older film body. The whole grip comes right off.
That's a nice camera, by the way. My dad has an SF-1N and I love it!