This battery case holds 2 AA batteries and connect them in serial so that you can use as a portable power for your project.

There wires are terminated with 2-pin XH 2.5 mm pitch connector that you can connect to the compatible receptacle on your board. It also fits the common 2.54mm pitch header. Pay attention to the polarity of the connector (red for positive, black for ground). You might need to swap the wire position on the connector which can be done easily using a pair of tweezers.

The batteries could add up to anything between 2.4V to 3V depending on which AA battery type that you use, alkalines or rechargeables.