Yellow battery indicator keeps flashing yellow

My 2 year old and rarely used SoundLink II keeps flashing the yellow charging indicator. Battery level is at about 40%, and it’s working properly.

I can’t set it to ship mode, as it immediately thinks it’s charging after holding the function button and removing the power supply.

Also a factory reset did not help.

When connecting to a charger, it will draw 500mA (the charger could provice about 2A).