Question about battery cell

[jeplane]

Bare with me, because I couldn’t get the screenshot on time.

Take a look at the picture and imagine the last cell on the right RED instead of amber.

Because I’ve never seen this before, but heard about it on this board, I would like to know if I should throw away this battery.

It has no swelling.
It has been charged 25 times.
It was made on Sept 2018.

 

[jeplane]

Now I am home, and restarded the battery.
The cells look good again.
Now what?
Thanks guys...

 

[BD0G]

Put it in the Mavic. Fly at a low hover till battery depleted to 20 percent. Change the Low Battery Warning to 20 percent for this. Land. Charge. Observe cells again. If no cell is more than 8-10 percent different then the others -fly it.

 

[charliesRig]

Not bad I would fly with it
It looks to me that the battery in question was discharge to the point were the last cell was down to the point were it was the first into the yellow @ 3.1v vs the best cell was 3.6 v not that drastic
A 0.5 on a half discharge battery

Personally would not fly
with less then %20 battery life

I would charge it up let it sit for a day
Put in your bird and check the cells
See if any are all within but no more than 0.7v
Then fly it down to 20%
then again check the cell diffrents

cR

 

[BD0G]

Edited my post above to reflect the .7 volts difference that CharlesRig mentioned above. I think we have the same idea. If one cell in the pack differs greatly from the others after a full discharge and recharge then there is cause for concern.

 

[Meta4]

It looks to me that the battery in question was discharge to the point were the last cell was down to the point were it was the first into the yellow @ 3.1v vs the best cell was 3.6 v not that drastic
A 0.5 on a half discharge battery

Edited my post above to reflect the .7 volts difference that CharlesRig mentioned above. I think we have the same idea.

**Arithmetic check time**
3.66V - 3.61V Between cell difference = 0.05V
0.05Volts is nothing.

 

[jeplane]

Thank you gentlemen.

I think when it was red, it went as low as 3.3.

This would be 0.3V difference. Is that when you start to keep an eye on it?

I will see what happens after the next charge...

Thanks again.

 

[Meta4]

Your recorded flight data will show battery levels for each 1/10th of a second of the flight.

 

[Drone-Retriever]

Now I am home, and restarded the battery.
The cells look good again.
Now what?
Thanks guys...

Jeplane,
You have a bad or failing cell.
You should look at the voltage under load when your battery is at 20%.
You said no swelling. Be aware you cannot see swelling unless it is the bottom cell which is attached to the label on the bottom of your battery pack. If the cell that is swelling is the top battery/cell then you will not see it. I would expect that the top battery is your issue.
Be aware if your voltage is dropping at 20% battery level then you should consider 20% as "out of power" and make sure you land prior to reaching 20%. Also the 20% point will increase as battery becomes worse.
Hope this helps.

 

[WithTheBirds]

A 50mv voltage difference is within the limits of what should be expected- particularly towards the end of a flight. GO4 will report a cell broken error in most cases where you have an issue.

What you should be looking for are other indicators;

Reduced flight time
Propulsion limited warnings
Rapid drops in depicted remaining charge %
Unusually warm pack after flight
Reported battery life %
Significant reduction in last reported usable capacity
Increased self discharge

If you haven’t used it before uploading your flight log at airdata will give you access to some useful battery parameters.

From what you have shared here I would not be overly concerned.

 

[Oconnb910]

Is there any place that shows what the insides of the mavic 2 battery looks like?

 

[Oconnb910]

The reason I ask is because we are talking so much about swelling batteries and things like that and people are panicking when they feel that swelling on the bottom but from what I can tell there is a gap between the bottom of the battery and the actual workings of the battery and I'm thinking it's a defect in the casting of the plastic casing of the battery rather than actual swelling of the cells.

 

[Oconnb910]

go one step further in my mind if the batteries are swelling like that it should be a cause of some kind of error and that should reflect in the cell conditions example voltage is in the go 4 app. I now have two batteries that are swelling on the bottom a bit and they show up fine as far as condition of battery. I would hate to throw away two perfectly good batteries because the bottoms swelled not indicating at the factory battery but rather than a defect in the plastic casing.

 

[DanMan32]

I doubt it has to do with the case, but we'd know only by opening one up.

 

[Oconnb910]

I doubt it has to do with the case, but we'd know only by opening one up.

And that is exactly my point because I have so far tried using a clamp on the battery while it is still warm and it seems to help. if you push on the bottom of mavic 2 battery there's a pretty good Gap there before you feel anyting. I find it hard to believe that the cells are expanding that far and deforming the case.

 

[Oconnb910]

And that is exactly my point because I have so far tried using a clamp on the battery while it is still warm and it seems to help. if you push on the bottom of mavic 2 battery there's a pretty good Gap there before you feel anyting. I find it hard to believe that the cells are expanding that far and deforming the case.

I have ordered two more batteries just to be safe but I am going to open one of these cases just to see if my theory is correct. I really hate to think that I am correct because so many have felt their batteries were defective and ordered new ones just as I'm going to.

 

[Meta4]

Jeplane,
You have a bad or failing cell.

So far there's no evidence to suggest this.
The OP would have to supply flight data to be able to see if there is any cause for concern at all.

 

[WithTheBirds]

The reason I ask is because we are talking so much about swelling batteries and things like that and people are panicking when they feel that swelling on the bottom but from what I can tell there is a gap between the bottom of the battery and the actual workings of the battery and I'm thinking it's a defect in the casting of the plastic casing of the battery rather than actual swelling of the cells.

For the battery to deform to the extent it can cause the latches to disengage (as has been demonstrated) it needs a force acting on it from inside. Cell expansion would seem to be the only logical cause. It is very unlikely the moulding process or material composition are implicated here. It might be a design issue, there could be insufficient internal free space to allow for call expansion. It is not uncommon for LiPO cells to perform well electrically even with some physical expansion. I have bare LiPO’s that perform very well (rc heli use) even though they come down with noticeable swelling.

 

[WithTheBirds]

I have ordered two more batteries just to be safe but I am going to open one of these cases just to see if my theory is correct. I really hate to think that I am correct because so many have felt their batteries were defective and ordered new ones just as I'm going to.

If the battery is deforming in use to the extent it might disconnect in flight it is defective.

Please post images when you perform the disassembly. It might be there is a mechanical modification that could make the battery usable.

I would discharge the pack and make sure you perform the disassembly somewhere that if something goes wrong you can allow it to vent safely.

 

[DanMan32]

I took my worst one apart. It's really tight in there.
They have very strong double stick tape on the bottom to the bottom battery, and on the top under the switch/light board to the top battery. The two outside batteries easily move apart from the two inside ones because of the outside ones stuck to the shell. If it weren't for that separation of the battery pack, it would have been impossible to get the case all the way open.

I had to use stiff but flexible plastic, a laminated list of IT teammates about the size of a credit card so that it could bend around the side of the battery to the back of it and cut the sticky tape holding the bottom battery to the bottom shell. The top one is stuck on pretty good but it's a smaller patch of tape.

There may be some gap between the batteries and she'll when new, but no gap when it swells. The cells may be double lined or loosely sealed as they are a bit squishy, but there's definitely captured gas inside.

Undo the ribbon cable at the circuit board that goes to the switch/lights. There's some silicon caulk at the socket.
Right next to the socket are two black wires from the circuit board to the battery board. I believe that's the temperature sensor. Try not to break them like I did. I believe that's why charge status now shows 1 LED when it was three, and turning on goes through the motions of the 4 LEDs but doesn't stay on.

The shells do latch together but there does seem to be a thin layer of adhesive along the seam. Looks like a bit of crazy glue. That's probably what makes it hard to unlatch them. That and the battery pack stuck to the shell backs on both sides.

The connector is held down with small screws deep inside but easily accessible. A strong flashlight will help. Besides the screws, the connector is latched onto the shell. A spudge can break that free.

What clamping might have done is shifted the gas to the sides of the pack. That probably won't last, especially with heat expansion.

I was tempted to use a metal screwdriver to pry the batteries from the shell, but I used a credit card, laminated card, and plastic knife. I didn't want to chance shorting out anything or puncture the cells. Even prying the cells loose had me a bit nervous.