ATTENTION! Handling battery Li-pol as described in this article is dangerous. May damage health and property. Improper handling can cause a fire and cause you or someone else serious injuries or death. Therefore, think twice whether to start the activity of this and where it will do. I recommend strongly to do this outdoors away from flammable objects and materials. Wear protective goggles and gloves. Below are examples what happen in the event that there is a short circuit or mechanical damage to batteries or to improper charging. Carefully look at these videos before you start !
I bought in China Lipol Turnigy Battery 2200 mAh 3s1p and found that one cell is broken. Its voltage does not exceed 3.7 V during charging and charger always interrupted charging. Because I was not sure the claim success in China, I tried to minimize the loss and damaged cell to exclude. I have no new one with the same capacity, so I made a 2s1p from 3s1p. Look how i did it
First, carefully remove the top plastic container in which cells are packed. Topmost part of it can be destroyed, others must be dismantled without damage, because we will use it again!
Middle cell was defective. When I thought about how to remove it, first I decided to unsolder it. But it can be quite dangerous, because of short curcuit risk. Cutters would have been appropriate, but they are too large and could cause a short circuit of one of the cells. I finally figured out that the pins are very soft and can be cutby the ordinary nail scissors, which better fit between the cells. Still, i made short-circuit of one of good cells. Fortunately, just for the moment, so cell is not damaged. One must be most careful, because short circuit can occur not only to demage to cell, but also injuries and fire ! Constantly think about the next move is going to do, whether it can cause a short circuit ! Keep in mind that the cells are connected on the circuit board and are constantly alive.
From the bottom of the circuid board I insulated cuted pins. I put a piece of EPP between the remaining cells order to save form and avoid deformation of cells. Better would be to completely dismantle the entire pack, unsolder all the cells, cutt off the board and solder back the good cells. Although the reduced size, but it is too laborious and each manipulation with the cells, moreover, increases the risk of cells damage, over-heating them during the soldering or short circuit in the handling of solder iron and so on. I chose therefore easiest variant, leaving the board as is, and instead of a defective cell I solder a wire. ATTENTION! It is important to choose a sufficiently strong wire with silicone insulation to withstand high currents. Weak wire could heat up and melt and damage not only the accu pack (short circuit) but also whole model!
Finally, I have everything thorough insulated and put back cover that I attache with a fixing tape. My battery is recharged without problems and it seems that the whole story ended successfully.