Mavic Air Battery won't charge. Need help please.

[Keithg1]

For a second time now, I have a battery that, after a month or two of non-use, refuses to charge. The charger blinks green three times then switches to red. When I press the battery switch, nothing happens at all.
I have 4 batteries and they have been recharged in the region of 50 times each and I'm now down to 2 workers. They've never been dropped or mal-treated.

Any advice please folks.

 

[Detritalgeo]

I may guess that there is one of the 3 cells that is out of balance so not safe for full use. I am not certain if this battery has auto-balance functionality.