TB47 Batteries - Reduced Capacity

I have a question about two TB47 batteries I am hoping someone can answer.

Two of my TB47 batteries have been charged approximately 20 times each and when I used them to fly with last I had a warning to say that they needed a complete discharge (to 5% or less) on the next charge.  This I did and after they were charged it said they were 100% charged but the indicated capacity had dropped from 4500mAh to 4244mAh.  The full readings I am getting is the total capacity is 4244mAh, remaining capacity is 4244mAh, charge is 100% and the battery life is 98% for one and 100% for the other.  The cells for both are all in balance.

Therefore, my questions are:

• Is this normal and is it safe to fly with them?
  

• Is there something that can be done to restore the capacity by discharging and charging?
  

• Are they faulty and need replacing?
  

I do not want to fly with them until I can confirm it is safe to do so and any advice on this will be gratefully received.

Seeing a slight drop in capacity doesn't necessarily raise any red flags for me.    These batteries will naturally lose capacity over time.  Just look at any laptop battery over time.  I'm a little surprised at the percentage drop for just 20 charges, though.  I don't trust the intelligent code in the batteries, for many reasons.  I hope that DJI will address the fault in their firmware, but until then, I would take the capacity readings with a grain of salt.

My question regarding your warning:
Were you completely discharging them every 10 charges?  That's the manual recommendation.   No biggie if you didn't.  Just curious on your usage pattern.

I'm not DJI -- so don't bank on my answers below, but my take on your questions:

• Is it normal?  Yes.
• Safe to Fly? Yes
• Can I restore the capacity?  Not really -- if it's really down.  I'd question how much is really lost, given the history of the DJI battery firmware.
• Are they faulty?  Not likely.  I think you're good to go.
  

fhhowdy@gmail.c Posted at 2015-11-23 20:00
Seeing a slight drop in capacity doesn't necessarily raise any red flags for me.    These batteries  ...

Thank you for your considered response and you have put my mind at rest.

Call me naive but I did not realize that this was a characteristic of LiPo batteries and/or it seemed like quite a large sudden drop.

I have read on this Forum, written by one of the moderators, that 20 charges was the recommendation before a total discharge - whether this overrides what is in the manual I'm not to sure but it is the figure I have adopted.

I am in the process of obtaining my BNUC-S qualification so I can use the Inspire commercially - I have just the flight test to take.  Part of this process is to keep a battery log and by recording all of this information it will help me keep track of the capacity and the effect on flight times.

Sky Dancer Posted at 2015-11-23 14:37
Thank you for your considered response and you have put my mind at rest.

Call me naive but I did  ...

I may have an updated manual, but mine says that a full discharge should be performed every 10 cycles of the battery.  The battery should be drained through flight until the unit turns off and wont turn on again.

There are non DJI chargers out there that will supposedly deep-cycle the batteries for you, but I can't attest to their success.  There are several frequent posters on the forum that will probably speak up on this...or just do a quick search on here for chargers.

I agree that the percentage drop is a little high, but it may be more of a firmware issue than actual truth of the battery's performance.

On a side-note, I also do a full discharge/deep cycle anytime the firmware is upgraded on the battery.  I want to give the firmware a full chance to see the complete range of the battery and all cells.

PaulKerry Posted at 2015-11-23 15:52
Oh... by the way, take a look at HealthyDrones.com

They have some great facilities for showing ba ...

Great point.  I upload every flight and look at the battery and signal performance.

Yes, it is normal, and safe! The more you use lipo the less capacity is left every time. However you need to do discharge/charge cycle about every 20 flights

PaulKerry Posted at 2015-11-24 11:24
Would you consider 500 charge/discharge cycles to be approximately the expected life of an Inspire ...

you can check the battery life by LEDs when the battery full charged
And, yeach , you dont want to fly it when it's less 20%

Thank you to fhhowdy, Paul and Tim for responding to my question and adding to the thread - it has certainly brought up some interesting and valid points about battery life.

Paul - thank you for the recommendation for HealthyDrones.com and it is a resource I will start to use.  I agree that the paperwork can be a pain at times, however it does provide a record over time which can be used to monitor battery performance/flight times.

Michael.