Wow I guess it's time I replace my original Phantom 3 flight battery. Glad I had a 2nd one. About a little over a week ago I charged both batteries up with no issues in anticipation of possibly needing the 2nd one for some photos I was getting of a new location. Turns out I never needed to use the 2nd battery so it remained in my travel case back home for over a week. I went to update my firmware yesterday and when I put that fully charged battery in I got the message about a weak cell. After the FW update I let my phantom hover over some tall grass in the yard until it ran so low and auto landed. The blinking warning about the battery was going the entire time.. Recharged the battery and now only one of the LED's blinks. I really expected to get a lot more life out of a battery. Guess it's time to buy another one.