Hi Mike,
You still need to use 2 optos, U2 & U4, per board when using the slaves in analogue mode, All the U2 optos will be connected in parallel for the Max cell voltage cut-out. Think of this as a logical OR. The optos are required because the cells are at a different potential to each other. U4 provides the Min cell voltage cut-out, also connected the same. There is also a resistor that is moved as well, refer to the circuit diagram for the Analogue slaves, it is different to the digital slaves.
My slaves are connected to a control board that turns on and off the charger and controller as required. The low voltage cutout is set about 400mv above the lowest allowable voltage for the cells, so 2.4 volts for the 2.0 volt limit the manufacture specifies. My
EV Managment Module controlls the charger through a mains relay. Whjile driving, when a low voltage signal is detected illuminates the battery light on the dash. If after 5 seconds the warning is still present it shuts off the controller. This allows you to back off the throttle to put out the warning. In practice I have been able to get the warning to come on with the batteries 70% discharged, at full throttle, climbing a long hill. Backed off the throttle and warning went out, without having to lose much speed, I might add. The deepest discharge I have done is 88%. Because the batteries were getting low I took it a little easier and never had a low voltage warning.