Ok I'm decoding this voltage thing for myself. The voltage chart above is for Lithium Ion batteries whose voltages are a bit higher and drop off more, faster,
than LiFePO4 batteries.
During charging or discharging it is not accurate to determine state of charge from voltage. After a rest of 30 minutes or so voltage should give you a pretty good idea of state of charge with Lithium ion. LiFePO4 stays much more flat overall but mostly in between 100 and 75 percent state of charge using the voltage chart I found below.
The balancing part of the BMS needs the voltage of every cell in order to balance them. So accurate that somewhere I read the wires going to each cell have to be the same lengths no matter how far from the BMS each cell is to keep the voltage readings accurate.
Here is a state of charge voltage chart I found specifically for LiFePO4 batteries.
Now I apologize for hijacking this thread in my confusion and it seems another about the different lithium batteries might be in order.