Major deviation - TB47 battery

Mr Phantom · Nov 12, 2017

I have a TB47 battery with only 21 charge cycles.
I was out flying yesterday, it was about 5 degrees celsius outside. After around 5-6 minutes of flight time when i looked at the battery page i noticed that one of the cells had a significantly lower voltage. I took the i1 back and landed.
Today i checked the flight log in Airdata and saw a major deviation that was 0.098 V, isn't that pretty big deviation, since a deviation of only 0.007 is considered a major deviation?
Can it be the cold weather or can the battery be defective? Is it safe to use it? Even though it was a little bit cold the battery was taken out of the car and used directly.
Another thing to note is that i haven't used this battery often, thats why it has only 21 flights even though its 2 years old. But i have been charging and discharging it every couple of month when i haven't been using it for longer times, and storing it at the correct voltage.

Mad_angler1 · Nov 12, 2017

The Inspire packs are 2P6S so you have a pair of cells in each bank, 2 years with little use is a long time and I suspect one of the cells is gong weak, you can try cycling it 5 or so Times from 100% to below 5% and see how it is but I suspect it’s for the trash.

Just be very careful if you do flying it to try the above, I would simply hover it a foot or so above the ground with no camera to discharge it.

Scoobywrx05 · Nov 12, 2017

Yeah that’s a good dip. Does the app say it has a bad or broken cell?

Mr Phantom · Nov 13, 2017

No the GO app did not say anything about a bad or broken battery cell, and no other warning meassages either?

I noticed that when i landed and the motors were on idle the voltage went up to 3.80 something and at that point the cell voltages were the same again with only a difference of 0.001, i.e. normal.

I don't know if it makes any difference but the major deviation was at 00:02, that means the deviation must have been at idle before the craft even left the ground?

But shouldnt the number of charge cycles be more important than the age of the battery as long as the battery is stored at the correct storage voltage. Maybe 2 years is considered a very long time even for LIPO batteries stored correctly?

Scoobywrx05 · Nov 13, 2017

Mr Phantom said:
No the GO app did not say anything about a bad or broken battery cell, and no other warning meassages either?

I noticed that when i landed and the motors were on idle the voltage went up to 3.80 something and at that point the cell voltages were the same again with only a difference of 0.001, i.e. normal.

I don't know if it makes any difference but the major deviation was at 00:02, that means the deviation must have been at idle before the craft even left the ground?

But shouldnt the number of charge cycles be more important than the age of the battery as long as the battery is stored at the correct storage voltage. Maybe 2 years is considered a very long time even for LIPO batteries stored correctly?

Not using them will kill them also even if stored correctly. The charge cycles does matter but letting them sit dormant for months isn’t the best for them either. Like I said check the actual voltage of the cells with and without a load on them . More than likely it was just a glitch at start up and the battery is not actually junk but if you are seeing a major drop in voltage in one of the cells after a few minutes of flight it may be one of the cells that are paralleled together is bad. You don’t really even need to fly it for a few minutes, a full stick up for 10 to 15 seconds watching the battery voltage will tell you if it has a bad cell or not. The temp you are flying in is at dji s cutoff point to have the battery warmer pads on and the cold weather will affect the voltage more than you think it would. If it’s 5 c on the ground you should have them on because it’s only gonna get colder the higher you go unless you run into a thermal which I doubt you would be flying that high.