All the 3914 with LEDs will do is make the equivalent of a voltmeter.
The fundamental question you need to ask is:
Can I estimate the power remaining in a NiMh battery pack by measuring its voltage?
Everything I know about NiMh batteries suggests that this is not a very reliable way to estimate the power remaining. In other words, the relationship between voltage and remaining capacity is highly non-linear.
There are battery fuel gauge ICs that mathematically integrate discharge current vs. time to display Ah used/remaining. Assuming your dive light is not continually switched on/off, a simple timer is a better way to go. If your light is turned on/off during use, then a simple count-down timer which is started/stopped with the light will work better than the voltmeter idea.