Battery Recommendations..

I bought a Group 24 for my Dart Sport and for the Swinger and should be appropriate for your Demon.
I usually trust Interstate but on my most recent purchase I went with the Ever-Start from Walmart since I was gonna make a 'resto' battery out of it.
I think Interstate MTP series is about $220 now except for the M series or budget line (less CCA and less warranty) which might be $140 or so.