I hope this reaches and/or found by anyone looking for an answer, as I have I have read much here and other sites regarding battery maintenance and problems with lights blinking 3 times and will not charge. I put my both my P3Ps in the closet 5 years ago where they sat until now, and just recently (due to all the free time Covid has allowed) got an itch to start flyiing again. I have five batteries, four charged to 100 % and I'm getting an average of 22 minutes (highest being 26!! basically hovering at a baseball game) from each in varying conditions.
My only issue with charging was one battery and it was the only battery that had errors (2) which occured from the first ever flight/charge.
I think I will try a possible remedy that Nigel over at  phantompilots.com :  
https://phantompilots.com/threads/phantom-battery-wont-charge-led-blinks-3-times.81815/

"Clip to the main power leads and charge as a NiCd till voltage is about 12.0 or slightly more but not over 12.6V. This way you have brought the battery to minimum level for DJI charger to accept.... or LiPo charger. Why direct to battery leads internally ? To avoid the board refusing to pass charge ...

Ideally it would be good to do cells individually but its difficult on a DJI battery as the balance plug is very small and does not fit normal LiPo socket etc.

Honestly - if you do not know how to do this .. are unsure ... best NOT to do it."

UPDATE : SO MUCH FOR THE SMILE I HAD ON MY FACE !  3 (FULL BATTERY) FLIGHTS WITH ONE OF MY P3P, 1 (FULL BATTERY) FLIGHT WITH THE OTHER, WHICH BY THE WAY WAS THE FIRST TIME EVER FLOWN !!! ...NOW ONLY 3 BATTERRIES WILL TAKE A CHARGE AND TO ADD INSULT TO INJURY, HAVING DONE NOTHING BUT CHARGE BATTERIES, BOTH BIRDS ARE DEAD !! (CAN NOT CONNECT). AFTER SPENDING 8+ HOURS WITH SUGGESTED FIXES, STILL NOTHING. I TRIED UPGRADING BIRDS FIRMWARE FROM 1.1.9 TO 1.11.0020 WITH NO ISSUES (I KNOW I WILL LIVE TO REGRET), BATTERIES UPDATED WITH NO ISSUES, BUT THE CONTROLLERS WILL NOT UPDATE (YES, I DID TRY UPGRADING AS DJI AND OTHERS RECOMMENDED 1.02.0006 THEN 1.03.0020). NOW, MY QUANDARY...HAVING FRIENDS OVER THIS WEEKEND FOR A BONFIRE AND DRINKS, DO I TOSS THEM IN THE FIRE OR DO I SEND THEM OUT AND GET THEM BACK NO BETTER THAN WHEN THEY LEFT.

Hello there greenbean. Thank you for reaching out and for sharing these information with regards to the DJI Intelligent Flight Battery. Great information and please stay safe always.