cr2032 Battery holder
Holds two 20mm coin cells (2032 are the most popular size) in series to generate 6V nominal. 20mm coin cells are popular as they are used in many battery-operated products, so they are easy to get, and fairly low cost. They tend to have about 220mAh capacity so this holder would give you 6V @ 220mAh with two cells. It features a black and red lead and an on/off switch.
cr2032 Battery holder specification:
double color lead with red and black (150mm long)