Fix for Lenovo LP40 wireless headphones not charging, also generic A6S headphones / earbuds.

I had not used these earbuds for 6-12 months and suspect that the battery level had drained so low in the charging cases that a protection circuit may have activated. Neither set would charge when I tested on several wall chargers and I left them connected for hours. Then a few months later I decided to connect the charging cases to the USB port of my laptop and a few seconds later the charge light illuminated on both. I was then able to charge them on the wall charger.

I am not sure if this was just a coincidence or if the laptop actually provided a trickle charge or some other signal over USB and it reset the protection circuit (assuming that was the initial issue). The USB port I plugged into is also a higher amp port than the others in the laptop, perhaps that can make a difference. I can't guarantee it will work for you but certainly worth a shot, let me know if it works and what model of headphones you have.