I don't think the DXe has telemetry. On other models (i.e. the DX6e) you can use the telemetry settings to alarm you when your voltage drops. Depending on the way your ESC is set-up, you should be able to tell based on the way the motor sounds. On my B-Kit 20A E-Max BL/Heli, with stock settings, the motor rpm will drop and you can hear the difference in "Soft Cut-Off" mode. Still have enough power to land without killing the batteries. My radio has timer so for the aircraft without telemetry (i.e. the Champ S+) I can set the timer based on previous flights. I generally check the remaining charge after every flight with my batteries to see how much demand I'm placing on them and how healthy the battery is.
Interesting!! Is that something you bought, pre-built, or did you wire something up yourself with the LED? I know I've always just flown with a timer, and then check my batteries when I'm done, which usually shows me about 3.7-3.8 voltage, depending on how hard I've flown/what I've flown. I like to err on having MORE battery than not enough.
Thanks! Kind of a neat idea, just need to see if I can find something from somewhere other than HK (since it looks like it's out of stock, and because I have issues with them not getting parts to me in a ridiculously long period of time).