@GeorgeBoudreau, sorry I’m a novice, so I am not trying to change your opinion, so much as understand.
I think I understand the reason to isolate the circuits, but I don’t see the point of physically isolating to a different board. I did not look at the Batrium solution, but there are plenty of BMSs where they run the current into the BMS. The designs you and Stuart are debating have no current going through the boards. I mean, don’t support an onboard shunt.
With respect to physical isolation (2 boards) it seems like you are violating that with your relays. They will be able to have an unknown voltage with up to 5a of current x 4 relays, but you seem resistant to having ltc2944 (really cjmcu-294) on the same board, even if it is properly isolated electrically. The 2944, just needs low power sense wires. Yes, at battery voltage. Again, just trying to understand.
Also, those relays seem rather overblown. I mean 5a is a lot of current to signal some load or charger to stop, right? I guess, I am asking whether you are inviting pathetic solutions by enabling 5a of current. Why not use the TLP22A-2 (2 relays per chilp and they are THT)?
As one use case example, I have a solar “controller” that is nothing more than a relay and a diode to shut off the solar and it uses maybe 20mA. The 24vDC to 12vDC converter also uses less than 30mA. Both of those are at battery voltage. The charger has a different voltage, because it’s not connected to the battery until it has shore power, but it too uses less than 30mA for control. The inverter was the only pain in the butt. It has its LED display board wired in series with the switch, so it seemed to peak at like 150mA, but was quite variable.