CrossRoads:
This is the system I was discussing.
The MAX6921 might be used, or the other demux chips discussed above.
Note how each battery is connected to nothing until a relay is closed.
A change is needed in the the Gnd for the battery WOULD NOT the GND for the Arduino, demux, & relay coils.
The two would be isolated so that the measuring electronics only connect to the battery under measurement +/- terminals.
I've been learning/reading some more, and after rereading this, this is what I think I can make of it:
The MAX6921 could be used just to directly control up to 20 relays that each isolate 1 cell and feedback its voltage to the arduino.
both circuits are completely separated, so no common ground.
The way this circuit is drawn, it seems like there wouldn't even need to be transistors or resistances around the MAX chip to control the relays, is that right?
are the outputs of the MAX chips (I think 40ma) enough to close a relay?
grtz
T