Take two: I bought a new battery for 2.50 eur from Clas Ohlson, went back to home and removed the old battery… and then one of the tiny wires soldered in the chip broke down…! Ok, I tried to solder everything back together and it looked like ok but just did not connect to the iPod. Several trial-and-error loops later I gave up and bought a new 30 eur Nike+iPod set. What a waste of everything!