This is 18650 2A lithium battery charging and discharging module, its input voltage is  4.5V to 8V and gives an output voltage that is adjustable from about 4.3V to about 27V .
Vin can be connected to a 5v solar panel, then the BAT+ terminal can output 4.2V for charging 18650 battery, OUT+ side then can output adjustable voltage
 
Technical Specifications:
Input voltage: 4.5-8V
Output voltage: continuous adjustable 4.3-27V (Counter clockwise to boost voltage)
Charging voltage: 4.2V
Charging current: up to 1A
Discharge current: the maximum 2A
Output reference maximum current: 5V 1.4A, 9V 0.8A, 12V 0.6A
Quiescent current: about 0.5 mA
Overshoot protection: Yes
Over discharge protection: None (also can be said yes, because 2V cut-off boost but does not block the output, output has 2V)
Deadline boost:: 2V, depending on whether added the additional protection board
Size: 3.3 x 2.3 x 0.9cm