If you work a lot on the Viper, you may be tempted to power it from a power supply. At least I was, tired of swapping batteries (That thing consumes a lot, 600-800ma just sitting there, depending on camera use). And if you leave it powered up too long with batteries it will deplete them down to < 3V. Not good for Lipos to say the least.
I connected it to power supply at 4.0v. Worked great for several hours. Forgot to switch the power supply off one time, and it was connected for more than 10 hours or something . Next thing I knew the FC board was dead. On power up the LED’s light up and quickly fade, and that’s it. Sonix board and camera works fine.
Oh well, vagaries of testing. Can’t blame anyone but me for expecting that FC board could permanently last powered up for days. Might cut the arms, will have an extra set of 4 motors and props, and a nice and compact (although rather expensive) 720p IP camera …
On the battery discharge topic, I’ve definitely seen some of mine down to < 2.9V for being connected too long. Won’t kill the battery but significantly reduces its capacity and longevity long term. Was actually going to suggest to mod circuit to jack up voltage preventing over discharge.