In this article I’m going to describe how I modified the battery cell circuit for a TGY 5000 6S. Recently, a European Hobbyking retailer sold out these batteries, but they wouldn’t do unmodified, because all my equipment designed for 3S. Another problem was that there were no batteries with capacity that could meet my voltage requirements, and I couldn’t physically or financially afford to buy a whole batch of different ones. Therefore, I decided to buy these batteries and tailor them to my equipment. Please, do not comment on how correct my decision was, let it be on my conscience :))

Well, here is the donor, let's go:

Look at the wired end:

This is the circuit diagram of a 6S1P battery (please, excuse my poor drawing skills):

And I want it this way:

I'm talking about a 3S2P. Finally, we have a 10000mAh 3S 20C instead of a 5000mAh 6S 20C. Now I take it apart. I use a powerful soldering iron with a massive tip, slightly overheated. Also, I use a balance wire for a 3S with a connector (I bought a few at AliExpress). First, I unsoldere the original connector and the power wires.

Some of them are soldered, others welded.

As we can see, the welding is not good. Disconnect the soldered ones using a soldering iron, and the welded ones – by tearing them apart (very carefully!). Here are the 6 cells:

And this is a cell:

As seen from the image, the cells are past their best, but they are worth the price I’ve paid for them. Now we’re in for the nasty operation of putting solder alloy on the terminals, which lacked it. Though not very well, aluminum does solder, it just takes a bit of patience and skill. I do it in the following way: I take a slightly overheated big-tip soldering iron, smear it thickly with flux and let it cool down a little. Then I take the soldering iron and rub the solder alloy over the terminal to thrust it between the tip and the metal. The tip removes the protective oxide film, the flux won’t interact with oxygen, and the alloy combines with aluminum. At most, 8-10 seconds, and then - complete cooling! If you have a bit of skill, you can do it all in one go and make an at least 20mm2 contact patch. Quite enough for 100A.

Then we connect the cells in pairs and bind them together with adhesive tape. To provide better contact, I made a few ‘horseshoes’ out of a 2.5mm2 piece of copper wire, blanched them and soldered them on the top.

Put the pairs together in a block and bind them with tape.

The middle cell looks the other way! Pretty rough, but that’s no big problem, because the flux does not contain acid. To connect the cells, I used the same piece of wire, except it was paired:

Now all that’s left to do is solder the power wires and the balancing connector. I isolated the wired end of the battery with a piece of polyethylene (how else is it called?) and covered it with adhesive tape. And I dressed the opposite side in the original wrapper. Then I put the battery through the charge-and-discharge cycle to check it for dry joints. Now I’m ready to take off.
This is the translated version. You can read the original Russian article here.