I would like to have batteries inside my Arduino Accordion eventually. As I am still waiting for some 10K resistors to arrive from China, I have decided to see if I could find some batteries around.

I opened an old (and broken) laptop to see what type of battery it had inside. This is the one:

That is the best image I got from the Internet and the specs can be read.

Then I proceeded to open it (be careful to not puncture the Lithium Polymer cells! They can explode!). I have cut one thumb and an index finger in the process, be careful...

These are Samsung batteries model ICP103450S. I managed to find a nice manual for it.

Each one could hold 2000 mAh (when new, I don't know if these are dead or not).

Multimitre time and, as expected, they are sort of dead (they read between 1.7 and 1.8 volts). So I found a very interesting article describing how to "revive" these https://www.instructables.com/Recovering-Lithium-Ion-Batteries/.

It turns out that I don't have that fancy battery charger. What I have instead is this little module here:

So, according to this video, I can reduce the charging current from 1A to 130mA using a 10k resistor. This other video shows how to replace the resistor. Since this battery supports (when new) a charging current of 1700mA, this should be enough to charge it very very slowly and prevent an explosion (I hope!).

So, here is the board with the new 10k resistor:

And here is the video of the charging process (these clamp multimeters don't work so well with low currents, but we can see it is less than 1A now):

Now I am going to wait and monitor to see how it goes.

TBC...