The red charging LED indicator does not turn on

I followed the disassembly instructions on this page and managed to open the headset, but I haven´t replaced the battery yet. When testing the voltage with a multimeter, it says 3.2volts, and the headset indicated that the battery level is low. However, when connecting the USB charger, I have the same problem that the red charging LED indicator does not turn on, and when measuring the voltage while charging, the battery still says 3.2 volt. So my conclusion is the same as yours, it is probably not the battery but the charging board that has a failure. I haven´t found any instructions on how to replace that yet. I am re-considering if this is a sustainable repair or not...?