VEmpty should be chosen as the voltage at which components in the system will cease to function. This sets the voltage that corresponds to 0% state of charge. The typical range is 3.0V to 3.4V, but it can be set as low as 2.5V in some cases. Because lithium battery discharge curves turn sharply down near empty, the amount of extra charge between 3.0V and 2.5V is very small and there is not much benefit from setting VEmpty less than 3.0V.
To set VEmpty less than 3.0V in the evaluation GUI, open the Register Viewer and manually write the VEmpty register to the desired value.