I'm now looking at trying to make the simplest possible single cell stackable BMS.
why do you need a divider though, and a voltage reference in that case?
fwiw, this is a pretty deep rabbit hole though, and you should know how to program to work with microcontrollers effectively. I did sort out an assembly routine for the tiny44 once (same as 24), no hardware uart made assembly the only choice for timing (literally counting instructions). It had majority vote, and I reduced the frame size (below what a typical hardware uart would allow) so it would be good without a crystal oscillator, in daisy chain (tx of cell 0 goes to rx of cell 1, etc). Auto addressing (command packet had counter that each node stored and incremented and forwarded). chain functions, like just give me the max voltage in the string, or the min voltage, or the sum, plus individually addressable voltages, with room for a temperature reading as well (thermistor, with max and min chain commands and apa), plus an led to help troubleshooting (i.e. follow the chain till the led's stop lighting for network problems, or look for the blinking led to identify the battery in question) and sleep/wake modes.
It wasn't one cpu per cell though, but easily modifiable for such, it is literally just the cpu and an opto for bare minimum at that point since the voltage range is acceptable. Though you still may need a calibration step after assembly (and it might need to measure vcc and internal temp to be accurate).
so while "simplest" can be optimized for hardware, it doesn't make the software (the part you are avoiding
) simpler. Siloing hardware from software in microcontrollers while trying to optimize is a bad mix. If you can wash your hands at the programming side, then by the same token the programmer can wash their hands at the hardware side, and just make whatever you give them work, more or less, suboptimally.
Though I'm concerned that you are ignoring very relevant comments regarding methodology, as if you see fortune in this direction, and that is what kills batteries and floods the market with junk. I think you missed that ship by about 8 years though.