It's done via the EZ Scan Digital software.
To do it you need to be using Software Ver 1.05 and have the latest firmware version, Ver U1.5, installed in the scanner.
In the EZ Scan Digital software you, if you haven't yet done it, go to the Advanced Menu entry and enable the Show Advanced Tab option. Once you have that enabled then you bring up the Advanced Features tab you'll find at the bottom of the screen. There you'll find the Battery Indicatior / Alert Values `box' that will allow you to change the settings for both NiMH and Alkaline batteries values/settings for how the battery indicator on the display is shown and what the alert value that you want the scanner to use to warn you that you are `at the end of the road' for whatever type of batteries you are currently using.
There is at least one `thread' here in this forum that has some other user's values you might want to check out.