Looks like the original design did in fact only have a single temp sensor, even if they were managing individual cell voltages. Beats me how such a design ever got past engineering.
I don't understand why the airlines bought off on this Rube Goldberg arrangement. This hugely complex battery system clearly is unsuitable for the intended use and is an obvious hazard to safe flight. They threw KISS out the window and sacrificed safety on the altar of weight reduction.