Actually, just to provide you with a little more direction here, you can actually calibrate, by programming, the various levels of icon flash, and battery cutoff levels. You enter this mode by Pressing PGM then FUNC then F3 (GLOB). This is the Expert Mode. Scroll down with the arrow keys till you reach Batt Icon Cal. Here you will find the various levels (when selected) for NiMh, NiCd and Alkaline batteries. The values shown in the Easier to Read manual are default and then recommended settings. Please note, the values shown in the scanner programming are digital prog. values, not voltage. Here's the direct link:
http://marksscanners.com/106_197/106_197.shtml#Bat Icon Cal
Definitely easier to do with a program like Win500 and the cable. Never wise to set the trigger voltages less than 4 volts as below this value (1 volt per cell) can damage the batteries. Also, the 106 is a digital receiver vs. the 164 which is primarily analog. The circuitry will be more power hungry and will probably deplete the batteries sooner.