Li-Ion Nitecore 14500 (NL1475R) 3.7V 750mAh battery with built-in micro-USB charging port.
It has a LED that indicates the status during charging.
Specification:
Model: NL1475R
capacity: 750mAh
voltage: 3.6V
continuous discharge current: max. 2A
length: 49.5mm
diameter: 14.2mm
weight: 18.6g