Hello,
I have had my Mavic Pro for quite some time but it has not been used in ~12 months

I recently took it out and decided to charge all the batteries (I have 4)

3 out of 4 batteries charged no problem. The fouth battery will not charge.
They have all be stored in a dry moderate temperature cupboard (16-22deg Celcius)
The battery has no physical damage.

What I can see is that, after conencting the battery to the charger, L.E.D 1 is flashing around 15 times in fast succession, then stopping for a few seconds and repeating this process.
Leaving the battery on charge overnight does not change this.

If I connect the battery to the drone, I am unable to power on the drone.

I have uploaded a video showing what the battery is doing. Hopefully someone has a remedy as I'd like to not have to buy a new battery (Its out of warranty)
https://youtu.be/CFOABcrzoAY

I'd like to know the answer too. I just bought a brand new battery, the only one in my city and this is exactly what happens. I am so furious, now its gonna be weeks until I can get a warranty replacement. This sucks

Hi Vengeance, sorry for the trouble with the battery, how long have you stored the battery? If there is no response when charging overnight, it could be damaged. If the battery is still under warranty period, it is recommended to send for the evaluation.

bburtoninternode.on.net Posted at 4-28 18:07
I'd like to know the answer too. I just bought a brand new battery, the only one in my city and this is exactly what happens. I am so furious, now its gonna be weeks until I can get a warranty replacement. This sucks

We sincerely apologize for the unpleasant experience with the brand-new battery, if it is the same issue with OP, the battery needs the warranty service, we hope you will get a replacement battery soon, sorry again for any inconvenience caused.

DJI Mindy Posted at 4-28 20:27
Hi Vengeance, sorry for the trouble with the battery, how long have you stored the battery? If there is no response when charging overnight, it could be damaged. If the battery is still under warranty period, it is recommended to send for the evaluation.

Hi Mindy, Probably 12 months. The battery is not likely under warranty.

Can I get it repaired or replaced even outside of warranty?

Vengeance Posted at 4-28 20:40
Hi Mindy, Probably 12 months. The battery is not likely under warranty.

Can I get it repaired or replaced even outside of warranty?

If your battery has been purchased for 12 months, the warranty service is not able to be provided. It is recommended to use a new battery.
Besides, 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.