What's going on inside "multi-cell battery monitoring chips" from places like TI, that allow them to cheaply and easily display battery cell voltages of series strings, compared to how difficult it is to layout an accurate circuit for yourself to achieve this? With say, an Arduino or the likes...

I mean... those chips are SOOO tiny! On a breadboard, for example, you need voltage dividers... or opto-isolators... or other things I don't know about. Ends up being a large device. I've scoured electronics forums, battery forums, engineering forums, and no seems to have an idea/circuit that even competes with those tiny, cheap chips. How are they doing it?

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Thanks!