Hi All,
Really strange and scary one yesterday. Was out flying and all was well. About 800m from Home point. Flying in a usual bush location in sport mode and had 40% battery. Then all of a sudden a got a critical battery warning and the Mavic was doing a forced landing. The battery dropped from 40% to 0% in about 15sec. I lost complete comms with it and it did not RTH. I was freaking out. Long story short.......I was able to GPS track its last location and despite being in dense bushland I found it!!! Amazing. I am really worried though why the battery died in the way it did. I have had no problems like this in the past. I watched back the flight data and all seemed normal until that last 15sec. I havent had time to test batteries in controlled locaiton but anyone else had this problem???

How many uses has that battery seen? Has it been in storage?

Just return it. Warranty is for 6 month and less than 200 charges. If not then you can use it to charge your phone but DON'T use it to fly anymore!

I'm no expert but I believe every 20 or so battery cycles its good practice to drain the battery to close to zero then recharge to 100%. I think this helps keep the battery calibration correct.
This used to be a problem with earlier DJI drones - not sure if its relevant to the Mavic.

Sorry to hear about this case. Did the drone hurt by this? Have you sent an email to support@dji.com and reported this case to them? If not, please contact them and start a data analysis. We will try our best to help this out. Thank you.

Auspete Posted at 2017-8-20 17:28
I'm no expert but I believe every 20 or so battery cycles its good practice to drain the battery to close to zero then recharge to 100%. I think this helps keep the battery calibration correct.
This used to be a problem with earlier DJI drones - not sure if its relevant to the Mavic.

This is false with the P3 through mavic and P4

Thanks guys. Drone was pretty good. Just some minor prop damage. The whole mavic and batt are 4mths old. I hadn't flown for awhile but battery had been on charge

Also, is there anyway to get more flight data off the mavic now I have it back? I only have info on the app from the point it lost comms. Unfortunately I was recording at the time so no vision

HWCM Posted at 2017-8-20 23:53
This is false with the P3 through mavic and P4

still a good practice with smart batteries.  not specifically this number of times or that regularly.. but every so often to completely get them flat where the protection cuts all power even to the LEDs on the battery then charge it uninterrupted back to 100%.  this charge cycling helps calibrate battery if there is a bad calibration which doesn't have to be huge issue like the OP could just be no other change occurred but suddenly missing 5 minutes of flight time, charge cycling fully usually fixes that issue, assuming no damage elsewhere in the battery or cells inside are in good condition ... also cycling can, not always will, fix heavier cell voltage deviations by forcing it to balance out, as long as again, no physical damage to board, battery or cells.  

my recommended ritual to smart lithium batteries in high current situations like drills, saws, impact drivers is to run them down completely once a month, this works well for me as i have 3-5 year old tools that use lithium cells inside and they still run hard and good.. while other people start having issues after 1-3 years and i suspect because they slapp back on chargers right after usage regardless show much power is left and temperature.. or they leave it dead in back or shelf for months which is bad since internally they can slowly oxidize when float voltage drops too low....  as for drones, im not sure, since they are technically high current, but they also vary more often..   im going out on a limb here and assume its like a tool.. so its ok to run hard and get them flat as long as you within within reasonable time like few hours or next day plug it and pull back up completely..  it you dont usually fully drain it and charge at 20% mark and 30% mark, i suggest every so often, run it down, charge it up..it should be fairly forgiving..

my recommendation for lower current lithium, is not cycle it fully if you dont want or need to..  lower current situations like basic or pro laptops, tablets, phones stuff like that, you do have more breathing room with lower current, but still have limits.   however i do not suggest repeatedly running them fully flat all the time that tends to chew its life up more in long run, instead try to keep it afloat some percentage.  like activate power save modes at 20% and use it less until you get a plug.. if some massive change occurs in life of the battery and nothing else has changed, do a deep cycle..kill it till doesnt turn on again then charge it uninterrupted, and turned off (unless by default boots itself) until its fully charged.  however once problems occur with lower current usage Lithium batteries, usually a lot less forgiving and recovering runtime back can be hit or miss and more often then not once gone its gone..
  

trentsare Posted at 2017-8-21 01:20
Also, is there anyway to get more flight data off the mavic now I have it back? I only have info on the app from the point it lost comms. Unfortunately I was recording at the time so no vision

You can retrieve the DAT file for the flight using these instructions and if you upload it to DropBox and provide a link here I'll take a look at it. The correct file will have a timestamp that corresponds to when the flight occurred and will be at least tens of megabytes in size.

What you described sounds a little like what was discussed here, though it may not be the same problem. If it is, though, I'll be able to tell from the DAT file.

ImHereToCrash Posted at 2017-8-21 01:47
still a good practice with smart batteries.  not specifically this number of times or that regularly.. but every so often to completely get them flat where the protection cuts all power even to the LEDs on the battery then charge it uninterrupted back to 100%.  this charge cycling helps calibrate battery if there is a bad calibration which doesn't have to be huge issue like the OP could just be no other change occurred but suddenly missing 5 minutes of flight time, charge cycling fully usually fixes that issue, assuming no damage elsewhere in the battery or cells inside are in good condition ... also cycling can, not always will, fix heavier cell voltage deviations by forcing it to balance out, as long as again, no physical damage to board, battery or cells.  

my recommended ritual to smart lithium batteries in high current situations like drills, saws, impact drivers is to run them down completely once a month, this works well for me as i have 3-5 year old tools that use lithium cells inside and they still run hard and good.. while other people start having issues after 1-3 years and i suspect because they slapp back on chargers right after usage regardless show much power is left and temperature.. or they leave it dead in back or shelf for months which is bad since internally they can slowly oxidize when float voltage drops too low....  as for drones, im not sure, since they are technically high current, but they also vary more often..   im going out on a limb here and assume its like a tool.. so its ok to run hard and get them flat as long as you within within reasonable time like few hours or next day plug it and pull back up completely..  it you dont usually fully drain it and charge at 20% mark and 30% mark, i suggest every so often, run it down, charge it up..it should be fairly forgiving..

https://phantompilots.com/threads/battery-discharge-charge-question.113196/

HWCM Posted at 2017-9-1 22:18
https://phantompilots.com/threads/battery-discharge-charge-question.113196/

everyone has their own theories and methods on it.... seems not a lot of people understand lithium polymer based batteries.    the myth is that you should never fully discharge them... the reality is, with protection in place, you can most definitely discharge them to flat level where dont power on and recover them completely...  a poorly designed battery may not prevent leakage until lower range where physical mosfet protection on each cell kicks in..

the myth you cannot or should not discharge below 3.00 is a partial myth...  so many types of lithium poly batteries and each type has different amounts and types of "doping" .  as an example, the lithium batteries likely used in modern DJi products, Tesla vehicals, LiNiMnCoO2 batteries have a cut off as low as 2.50V per cell and can charged up to 4.35V with a high current operational range(10C and above) 3.0V - 3.8V and can be charged up to 3C rate per cell or higher (depending on doping) Dji has a operational cutoff of 3.00V and a physical cuttoff of power of 2.85V.    makes plenty of sense..

did your battery have an voltage  fluctuations across the cells ?

Did you freshly charge the battery before flying sport or was it sitting around beforehand ?
It's probably a good idea to recharge all batteries before flying just in case the capacity measurements get messed up, which can be the case