This battery is from my trusty old Phantom 4. It's been sitting for a  little more than a year ( I have two other batteries in the same state).  When I first checked it, it flashed 4 bars, then dropped to one bar. I  plugged it in, and it won't take a charge...it's been in this state all  afternoon...that is LED 1 rapid flashing for 18 flashes, then a pause,  then more flashes. It's charging inside on the standard DJI charger.  Battery isn't warm. Not swollen.

I don't have high hopes that these three are recoverable batteries, but  before pitching them I thought I'd post to see if anyone has any  insight.

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Hello and good day MacCool. I am sorry for the trouble this has caused you. Upon checking the video you have posted. I am sorry to say that the said intelligent flight battery is over-discharged and might not work properly again. The Intelligent Battery’s power will be consumed at a slow rate when it is being stored after being powered off for period of time. Also, the battery may become over-discharged if its power is critically low when being put into storage. To avoid this, we recommend that you discharge the battery to between 40% to 65% and store it in a cool, dry space ( at an ambient temperature of 22°C to 28°C ) when it is going to be idle for more than ten days. Check the battery’s power every three months and fully charge and discharge it at least once. Please perform this routine maintenance to keep your battery healthy. Thank you.

ti would ry turn on battery , one click and hold second click  , add the charguer and see what happens.
your batt shows 100% util life in the video

I agree with DJI Stephen.  The battery is likely not going to ever work correctly again because you stored it and ignored it for too long.

There is a small chance it would begin to charge if you attempted to turn it on while on the charger.  The video does not show you trying to turn on the battery.

There is another small chance the battery is in hibernation mode and will begin charging if you press the button, let go, and let it sit for five mins.  Then attempt to charge.  

If this was a bet, I'd put twenty to one that the battery is toast.

Good luck

I agree, the battery is more than likely dead due to the long storage time, you can't just leave batteries to sit for 1 year and expect them to work. Also the battery is not full, in the video you see him do the battery health check(Long press), this doesn't tell you much of anything, i believe it's based on the number of charge cycles your battery has done, or at least something along those lines.

Ben Mason Posted at 2019-12-31 01:14
I agree, the battery is more than likely dead due to the long storage time, you can't just leave batteries to sit for 1 year and expect them to work. Also the battery is not full, in the video you see him do the battery health check(Long press), this doesn't tell you much of anything, i believe it's based on the number of charge cycles your battery has done, or at least something along those lines.

Yup. All three batteries are in the recycle bin. They ain't coming back.