HelloAndy9. Thank you.
My 5 batteries were purchased at the same time at the end of May 2017.
I have other drones, the P4 Pro flew only two hours in total: the faulty battery, like the other four, was recharged 4 times.
Then that battery just comes to its end I think. Much depends on how the battery was maintained, was it stored at right percent of power, in the right environment, etc. They say that not using it is not very good for the battery.
Yep. Not using is not good. HOWEVER! IF you do it correctly one can store BATTS for quite a while.
Here is what I found.
I read that the sweet spot for long term storage is in the 50% ranges. I will agree with that.
Back in June I had a career change followed by a job change with no time to fly. I read that every two weeks is recommended.
I became a little concerned after 4 months of not cycling the batts at all 8 batts in total.
Before long term storage, I flew all the Batts down to 20% Landed. Then I ran them down until the drone powered off. Totally legit to do by DJI recommendation. Also read all of that was good to reset the batteries as well.
I then charged each batt to roughly 53 to 55%. DO NOT STORE THEM IN ANYTHING AIR TIGHT. Ask my how I know that is one of best way to destroy a Lippo. lol
So they were stored at roughly 70 degrees at those voltages. From October to Mid Feb. I simply topped them off and flew each batt (Took a while but thats what you do with 8 Batts)
I repeated the process down to 20% then down to shutoff. Then I recharged to full and flew them again down to 20 to 25%. Uploaded all the data to AirData and to my suprise my batts where in EXCELLENT condition. They all had an average of 40 charges and were new last May (2019).
So to recap, the above procedure worked well and is what was suggested.
Before I knew how to properly STORE the batts, I had ruined 3 Batteries I had before by not flying. Leaving them fully charged. (DO NOT DO THAT), and never letting the batts go from full charge to no charge every 20 flights or so.
One last note. So what I do now is after flying and the batts settle down. I go WAY longer than needed. I will bring all levels of charge to 53 to 55%. I never know how long it may be sometimes between flights.
Well, depends on what batt you are using. The Phantoms batt. has its self discharging algorythm so no need to bother with those percentages. After full charges they will automatically discharge to 50% after a few days and that is adjustable.