Check out the linked pdf doc.
Wow, +-250V CMRR. That's impressive.
separate Arduino processors, powered at different points in the battery chain, and each reading 6 A/D channels,
I also was thinking about this overnight. I thought that my above design could be modified to handle either 6 batteries (although 6x15v is getting too high for good resolution) or maybe "12 volts" where that is made up of various combinations, 6x2v, 3x4v, 2x6v or 1x12v.
You would then hang boards at various location on the battery string as required. In the case of this thread's application that would mean 3 batteries per board or 15 boards, maybe as few as 8 if you up the range per board.
Another option it to incorporate a special monitor chip like the 12-channel MAX11068, they can only handle 5v per cell which is no good for me but would work here. Also there's the LTC6802.
Rob