Hi @UltraFred,
This isn’t something I’ve looked into in depth, but from a brief search the closest potentially relevant thing I found was some automotive battery monitors from Texas Instruments.
If that’s not a fruitful path then likely your best bet is setting up an ADC + resistor combo and multiplexing between the packs (or even between the cells). The voltage generally shouldn’t change super quickly, so it should be sufficient to just repeatedly cycle through the measurements instead of needing several ADCs to measure all the packs (or cells) at the same time.