I have this circuit and I do not understand the purpose of the diode connected to the ground. This is a Bluetooth device (works at 3.3v) that has a 4x 18650 battery pack and a USB charger. When you plug in the USB it supposedly charges the 18650 batteries. (4x 18650 batteries in series)
The diode(?) is connected via the yellow wire from battery ground, onto the board, goes passes a few capacitors and arrives at a chip with marking "MPEK 2517 A023" (or AO23) and an inductor right beside that chip.
When no USB is present the end of the yellow wire inside the white socket measures 0V. when USB is plugged in it measures about 2.1 volts steadily decreasing while the voltage steadily increases. (about 0.0001 volt every 2 seconds)
Can someone explain the purpose of this diode? thanks