This is a Chevrolet Volt battery. The black box on top is the BECM (Battery Energy Control Module). There are six plugs into it that monitor 16 cell groups. A cell group is two 3.7V Li-Ion cells in parallel. Each cell group is monitored by the BECM, and there are 96 different OBD codes (Check engine light). The cell groups are all wired in series giving a total of 355V.
Here is a video of the dissection of a Chevrolet Volt battery, right down to the individual 3.7V cell.