I've had probably less than 12 flight sessions (each session being all three batteries). I've always landed at 20% or more left on the battery. Always charged them with a genuine DJI charger. Always kept the batteries charged and stored safely in the Go Professional Case where they're not going to be damaged, heated, chilled, bashed around, or otherwise given a hard life. However, when I plugged the quad into the Assistant software the other day, it mentioned that the battery in the quad had a faulty cell, and advised discarding it. But it never said that again. I plugged it in a couple more times, and never got this warning again. I marked it as "Suspect" and put it aside to use only with great caution. Today, I thought I'd give it a careful run, at low speeds, at low altitude, and over ground only. Even though it was supposed to have been fully charged, and all 4 LEDs lit up, when I plugged it in, the OSD was saying just 71%. It then took some 5 minutes of flight before it moved at all, it stayed on 71%, then it dropped very rapidly, I could watch 0.1volts per second dropping on the OSD, and the percentage was dropping only slightly slower, down to about 50%, then it slowed and went at a normal discharge speed down to 20% I decided to let this one almost fully discharge just as an experiment, so then landed and left it on a high speed idle, just a whisker off lifting off, Until it was down to about 8% and then shut everything down. Tonight when I put it on the charger, it seemed all was going well, but then I found all 4 LEDs lit up and not flashing, which it stayed that way for a minute or two, and then it returned to flashing and working it's way up the LEDs sequentially like when it's freshly being charged, before finally stopping charging and turning off, some several minutes later. I'm going to throw the battery away. I'd rather throw away, even a perfectly good battery, than risk having the quad shut down mid-air because of a dodgy battery, and come crashing to earth or sea, because I was too cheap to throw away a suspect battery. It's really a no brainer. But it's made me wonder, how long a life should I get from a battery that is only a couple of months old, and seen barely a dozen discharges in it's life time.