A simple little protection board for low current (3A or less draw) systems using 2 series lithium cells. The type / size of cell is not important but the chemistry, must be lithium.
The Negative ( -) end of the first cell is connected to the PCB terminal marked B-
The connections between the (+) positive end of the first cell and the (-) Negative end of the second cell is connected to the PCB terminal marked BM (battery middle?)
The (+) Positive end of the second cell is connected to the PCB terminal marked B+
The connection to the load / charge is made to the terminals marked P+ (7.5V nominal) and P- (GND Negative)

Operation is simple. If either of the 2 series cells exceeds the upper voltage limit or drops below the lower voltage limit, the load / charge connection disconnects. The load / charge connection reconnects when the voltages are normal again. This may be the basis of a simple charge limiting circuit and over discharge protection circuit.

The board is well made and works as it should.
I hope this clears up some of the questions raised.

Nabíjací a ochranný obvod pre 2ks spojené Li ion batérie 18650 2S 7,4 V. Balenie po 5 ks.