Let's state that again using math. Charging has to stop when the charge current (Ic) is less than Ic = (Vc-3.370)/Rb, where
Ic = Charge Current Limit
Vc = Charge voltage
Rb = Battery internal resistance
Stated as a proportion of the cell's capacity, Ip = Ic/C, where
Ip = Charge Current per Capacity
Ic = Charge Current Limit
C = Rated Cell Capacity
The reason charging has to stop is that the cells are full and can no longer move lithium. For my 230 Ah cells with an internal resistance of ~0.024 Ohms (24 milliOhms), the charge current limit looks like this at a few different voltages:
Vc | Delta | Ic | Ip |
3.650v | 3.650-3.370 = 0.280v | 0.280/0.024 = 11.46A | 11.46/230 = 0.050C |
3.500v | 3.500-3.370 = 0.130v | 0.130/0.024 = 5.42A | 5.42/230 = 0.023C |
3.400v | 3.400-3.370 = 0.030v | 0.030/0.024 = 1.25A | 1.25/230 = 0.005C |
3.370v | 3.370-3.370 = 0.000v | 0.000/0.024 = 0.00A | 0.00/230 = 0.000C |
So, let's all say it once again: Once the charge current is below the calculated limit at your charge voltage, charging has to stop because the cells are full. Any impressed voltage after that *must* be at or below about 3.370v or damage will occur.
By the way, the first line above shows the cutoff at the factory specification, which is 0.050C at 3.65v. Since I have two batteries in parallel, I have to stop charging at twice the current shown above because each battery is taking half of the charge current.