I'm currently replacing the batteries and have been doing a bit of research on 8D's vs group 31s
Here's a few links comparing/discussing.
Do I need two 1100 CCA start batteries? - iRV2 Forums
8D or Group 31 Batteries - School Bus Fleet Magazine Forums
The guys at the shop said to put back in whatever was in there to begin with but i'm not sure what that was. It looks like most of the AARE Cummins 8.3 busses on this site are using 2-8D's. Thats seems a bit much, but i think the school bus batteries were oversized to allow the bus to run the flashers, etc for a while and then start right up. The cummins 8.3 only needs 1500 CCA i believe, and from my research it looks like group 31s are more common for that engine on other platforms. It makes me think the 8D's were chosen more for their reserve capacity than their CCA.
Two 950CCA group 31s should be able to easily spin the engine, even in cold weather, plus they're cheaper, lighter (and less maintainance?). For these reasons, I'm leaning toward downsizing (if you want to call it that) to the group 31's.
For all you other BB AARE cummins8.3 folks, what is your battery configuration? Any reason not to go with the group 31's?
In other news i've been getting some welding lessons for a guy who has a welding shop next to where i keep the bus. Welder comes this weekend and I plan to rosette weld the hat channels i've installed to give some added strength. This weekend i'll also be reattaching my coolant line and creating some templates for the transition section and end cap.
Man this is fun!