The red charging LED indicator does not turn on

Hi, it's now 6 month later and the fix I did still works. So I definitely can say, this problem is not related to charger, battery or any other active part. It's just poor soldering done by Sony. Hopefully new models are better assembled but probably not. It's not in the manufactures interest to do long lasting quality products. It's done to be sold. Period.

Take a look at the charge connector solder joints on the board. They are know to crack through time and connecting and disconnecting the cable. Might be something as simple as re soldering the connections.

@olsensan I think you are on the right way and I also believe in fixing things. Keep going with your excellent troubleshooting. The only thing I suggest at this time is that you get yourself an inexpensive USB Ammeter and see if your headset draws any amperage. Your battery voltage does not change which could be okay at 3.2V but lets see what happens when you plug it in and monitor the amperage. also, check the actual charging port to make sure that it is clear of any debris and nothing bend or corroded. Then try another cable and USB charger to see if that helps.