I set up two beacons on the top and bottom of my Citation (hero) jet that flashes the voltage of a six cell lipo as follows: 6 flashes if over 4 volts per cell, 5 for 3.9 volts an so on to 2 if over 3.6 and 1 if under 3.6 (empty). I made a video with a 10 cell battery, 6 and 4 cell. At the start it is flashing 6 times but then with application of part throttle it drops to 4 flashes as the smallish battery is running 2 90 mm fans and the battery drops below 3.9 volts. With the throttle closed the flashes go back to 6 as the battery is still nearly fully charged. The cool thing is that I don't need to look away to see how the battery is doing. The video:
The flashes are 35 milliseconds long so if your playback is dropping frames, you will miss flashes. This will be used on 10 and 12 cell series/parallel packs but will monitor one 6 cell pack which will tell the story.