Battery health in cold conditions

[Ralph thompson]

Not a new issue but would appreciate feedback from those knowledgeable in LiPo battery technology. I have 6 batteries for the M2P, the older batch of 3 are all around 60 cycles. All been carefully maintained and cycled about every 20 uses. All fully charged to 100% before use and stored after a couple of days at around 50%. But winter in Montreal can be harsh, operating in -20 deg C is pretty common and since I work as a journalist, I don't get to choose the days when drone photos are needed. I've had a few post flight shocks recently, there was no indication of a problem during the flight. The batteries were kept warm before TO and above 15deg C before climbing (a checklist item). These 3 examples are all the same battery.
Jan 3rd I saw after the flight some serious low volt warnings as low as 12.25V(I don't recall any warning during the flight). Ambient temp -15 deg C and the battery was between 60% and 27%. But would a low voltage on one cell cause the battery to shutdown?


Feb 26th big deviation with cell 4 more than 0.07V below other cell voltages (I fully cycled the battery after this event). Ambient temp -20 feeling like -25 deg C. Why does it draw down on cell 4 all the time, is it possible to fix this? (I see from other posts that this has been observed by others)


Feb 27th, battery fully cycled, but still a larger draw down on cell 4 after a few minutes and a spike where cell 4 deviated by 0.075 v



I appreciate that the low ambient temperatures are hard on the batteries but I'm wondering if its time to retire this battery? (No swelling or cracks). Of course this could be the reason DJI specify a minimum operating temperature of -10 deg C.

 

[old man mavic]

at very low temps the cell chemistry is affected and the flow of electrons is impaired which creates a high resistance in the cell ,so the battery is unable to sustain enough voltage to the motors, it seems that on multi cell batteries, it is mostly the last cell in the series that suffers the most from this phenomenon ,

 

[DoomMeister]

DJI Batteries and Cold Weather . . .

Some of you may know Ken Booth who was originally active with DJI and very involved in their Battery Design. : (the below is 100% from Ken Booth) "First please look at the attached image, this should really explain all you need to know on how cold effects capacity. Once you understand this...

mavicpilots.com

 

[Ralph thompson]

Thanks gents, I have read the Ken Booth post, it’s very helpful. But if, as I do, hover the drone at 5’ & wait for the temp. to get to 15 deg. then doesn’t that mean the battery is at a safe operating temperature? So from the battery perspective, it’s operating at a normal temperature. With the inspire you can see a graph of battery temp but it seems DJI doesnt make that available in the SDK with the M2P

 

[DoomMeister]

The best thing you can do is have the batteries stored in something that will keep them somewhere near 80 degrees F (27 deg C) until you are ready to use them. Possibly use a powered combination cooler/warmer.

 

[Ralph thompson]

Thanks good thought.

 

[mikegrad]

i would pick up a few of the self heating enterprise batteries for those days. they should work with the M2P

 

[slup]

...But would a low voltage on one cell cause the battery to shutdown?

A low enough voltage will eventually shut down the drone ... if it's still airborne that means free fall.

DJI use "Forced low battery auto landing" to prevent free fall ... if a cell in the battery goes below 3V it will kick in & force land your drone then & there without you being able to stop it.

You mentioned that you saw 12,25V as a total battery voltage ... that's an average cell voltage of 3,06V

Then here ... that's an average cell voltage of 3,09V.



You have been on the verge of experiencing a forced landing ... hope you're aware of that & fly so you don't damage anything below if it's going down.