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...for a few years, I was a person doing automotive electrical and electronical trouble shooting and (in theory) repairs. I have absolutely zero experience or knowledge of bicycle electromagical shifting systems. None at all, so take this with a shaker full of salt. They do seem pretty simple in design.

Those car systems (much more complex than bicycle Di2 systems) required little or nothing in the way of maintenance. That's the beauty of electronics. OTOH, when something went wrong (and when you are in the repair end of it, that's all you see), the repair costs were often quite high, and it was not unusual to replace stuff that was expensive. So I will probably not be buying something like that any time soon. But that's just me, and I am pretty old.