Not long ago an accident happened. During a crash, one of my best batteries got pierced.
The battery was the Dinogy 4s 1300mAh 65C. I was desperately sad. Right after the crash I examined the battery and realized that one cell got pierced by some piece of weed or such. There was a slight sweet smell coming out from the tiny hole.
I hesitated between a repair and a degradation of the battery to a 3 cell one, but finally I decided to give repair a try.
So I went home from the field and headed right to my garage. My first idea was to fill the hole with a two component epoxy, so I went for it. I simply removed some part of the heatshrink around the hole and applied the glue.
Not a long time after gluing the hole I faced to the fact that the gas, coming out from the cell simply got through the epoxy, that get half toughened by the time.
My next idea was to tape the epoxy tightly so it could keep the gas inside. So I taped the hole and waited around half an hour. When I thought the epoxy was hardened I removed the tape. Unfortunately, the hole was visible and the gas was still leaking through it.
Then I decided for the second round. As the previously applied epoxy filled quite a big area, even below the heatshrink I was hoping that time to be successful. So I mixed another batch of epoxy and glued the hole again. That time, I taped the whole area immediately after gluing and did it very tight.
After another hour I removed the tape and examined the result.
The gas could still make a bubble into the epoxy, but that time did not get through. Still, it was a question whether the cell survived, so I connected the battery to the charger and started to charge by approx 0.1C value.
And voila, when the battery got fully charged, the affected cell showed no difference in voltage.
Next day I went out to test the battery. I consumed approx. 80% of the full capacity, and have not realized any loss of power.
Since then, I flew that pack many times, without any issues and I have to say it is still as good as it was by the beginning. No degradation, no heating, no mismatch cell voltage. And I simply love the power that battery is able to deliver, time after time.
So, if anyone experience a similar problem, just know about the fact that it is worth to try fixing even a pierced cell. I am not saying it will be always a happy end but still, the epoxy glue is much cheaper than to buy a new expensive pack, so why not to bother with it? 😉
And a good advice to the end: always wrap the race quad battery packs with some tape or insulating material, that can save them from accidental piercing. It is much cheaper than to buy a new pack when it gets destroyed during a crash.