Battery (cell) charger with European round plug. The adjustable slider in the battery seat allows the charger to accept both 14500 and 18650 Li-ion batteries.

To use, place the battery in the charger, matching the positive and negative indications on the sides of the battery to the same indications on the charger, and then plug in the charger. If the battery is properly positioned in the charger, a red light will illuminate and then some time later change color to green when done. It's normal for batteries to get warm while charging. Best practice is never leave charging unattended then once the light turns green, unplug the charger and remove the battery.