While I did not read this entire thread, I skimmed through most of this, and I guess I'm just wondering why it is so important for this battery cart/station to be self-sustaining. You're supplied with power in your pit, specifically so teams can charge their batteries and driver station. I completely understand wanting to make an organized, well put together station for charging and storing your batteries, but the necessity for it running off a generator seems over the top.
Also, as far as making it able to drive, I see even less of a reason for this. Being able to drive the robot cart would make more sense then this, although I know I do not think that is a good idea, and I know many volunteers who have worked the queue at a competition would agree.
While I know that with all of the batteries, chargers, frame, etc. the cart will weigh a lot, I guarantee it will still be easy to push/pull.
Our team built a battery cart 2 years ago and it works great. Currently able to charge 9 at a time but could easily switch those 3 single bank charges to 2 three bank chargers. While it is heavy, we never have an issue being able to push it, and often times have other boxes on top of the cover when we are moving into our pit at the beginning of a competition.
https://www.facebook.com/media/set/?set=a.349869318365793.90542.109248172427910&type= 3
There are more pictures of it at this link and I would be more then happy to ask any questions you have about it.
-Nick