Hello, I was reading about batteries (for headphones, portable speakers...) and I realized that sometimes a 3 cable battery doesn't necessarily mean that the temperature sensor (3rd cable, besides + and - cables) is working correctly and being checked, but could perfectly be that the cable is a dummy one that gives an OK no matter what the temperature. In other words, it is an ON switch that has zero safety value, which is the only purpose of the 3rd cable.

So... that got me thinking... there are sometimes that you are not able to get the original battery, or that it's incredibly overpriced... and I asked myself:

What if instead of swapping the whole battery for the given device I am repairing, I "take apart" the original broken one, save the IC and solder the new battery (the "thick" silver rectangular pads) to the original IC? That should work fine, right?

I also thought that: What if the original IC is also faulty?
I know, I think that's pretty rare, but anyways... it could mean that all the hassle of taking apart the original to have the IC, do the same with the new one, solder the new "raw" battery package to the original IC was for nothing and have to assemble the new one with its worse IC but working one.

A battery like this, as an example:



Of course I would always swap it for a battery with the same voltage and same chemistry. In the pic example, a battery that is 3.8V (3.7 would work?) and is Li-ion.

 

Certainly replacing only the failed cells is a valid approach. There are some serious challenges though. Soldering to a battery cell will cause heat damage in the form of melted battery seals. I learned that the hard way quite a few years ago.