I was planning on not using my copter for a couple of weeks so I drained my batteries to about 25% to store them for that period of time.  I’ve researched treatment of batteries extensively on this forum as well as consulting with our local DJI distributor and this seems consistent with the recommendation.

After the ~ 2 weeks I fully charged both batteries but noticed my older one (14 charges according to the history) was down to 98% of battery life.  Since I was close to 15-20 charges where a “deep cycle” was recommended, I drained this battery to 10% and fully charged it back to 100% only to find out that the battery life had dropped to 65%! What the heck happened!  All cells show 4.3v and 100% charge.

I guess my question is; does anyone have any suggestions on how I can recover the battery life, and if not; is it safe to fly when the app says 100% charge but 65% battery life?

I've flown with a battery that said the life was 32% with no ill effects.  Flight time was still ~15 to 17min.  It has 58 charge cycles.  I drained it to 3.2 volts on the lowest cell then charged it.  Life went back up to 90%.

That's pretty strange. Short answer - maybe you should give it a couple of more chances to calculate.

I just checked mine that was charged up this morning. It's a year old, has 75 charges and has never been "deep cycled". Mine has finally worked its way down to 95%. I only have one battery. BTW - your voltages are higher and more even than mine!
I think you're golden!

Rnfaust Posted at 2016-3-18 13:39
That's pretty strange. Short answer - maybe you should give it a couple of more chances to calculate ...

Interesting that you should mention "time to recalculate".  I thought this would be instantaneous but, guess what...I fired it up this morning and it read that I had 100% battery life remaining.  I think you're right, it does take some time to calculate and I think I'm "golden".  Took her out this afternoon and everything was good.  Thanks for your reply.  I think I will be more patient next time before I panic.
T

Tomsbird Posted at 2016-3-19 08:57
Interesting that you should mention "time to recalculate".  I thought this would be instantaneous  ...

The battery life figure is not a measured value, it is a calculated value, and sometimes it gets it wrong. Nothing to worry about. The most important thing is that all you battery voltages are the same, that is a good thing.

Geebax Posted at 2016-3-18 16:10
The battery life figure is not a measured value, it is a calculated value, and sometimes it gets i ...

Thanks for the responses guys.  Much appreciated.

Somewhere on this forum, there are instructions posted for calibrating the battery.  They call for running it down to the point of shutting itself off and then recharging it fully.  I did both of mine several days back and all is well with them.  You need to be careful when you do the discharge.  Fly it down to somewhere ABOVE the critical point.  Then remove the props and run it down until it turns off.  It will take quite awhile while it is just idling, but is safer than trying to do it with props on.  Be sure to let the battery cool down before charging.

You might try putting your critical point at 0% (or as low as it will let you) and let it idle on the ground with the props off.  Be sure and land much earlier than that to prevent a disaster.  One of my batteries ran for quite awhile after reaching 0% on the metering page, but the other one quit well before zero.  I think what's being done by this procedure is teaching the battery program where the top and bottom of charge is so the battery level indicators are closer to real.  This is NOT a procedure to do very often.

.........  and don't forget to reset your critical battery setting  after you are done.  

AG0N-Gary Posted at 2016-3-18 20:00
.........  and don't forget to reset your critical battery setting  after you are done.

Thanks Gary.  It seems to me that I read somewhere on this forum that this "deep cycling" should be done after 15-20 charges; your note would suggest not that often?  Maybe this should only be done if you're having issues (imbalanced cells, poor battery life)?

Tomsbird Posted at 2016-3-19 10:48
Thanks Gary.  It seems to me that I read somewhere on this forum that this "deep cycling" should b ...

That's my read also.  I don't know how this "calibration" procedure relates to the more documented 20 cycle rule of discharging.  If you have been here long, you notice that some of these procedures have evolved from other people's experiences and failures.  Some have come along since I've been here and are not in the earlier manual.