Battery
Connecting the positive of one cell to the positive of the other, and the negative to the negative is called connecting them in parallel.  The voltage stays the same, but the current is added together.  Voltage is the pressure pushing the electrons through the wires, it is measured in volts. Current is how many electrons can go at once, it is measured in amps.  The combination of current and voltage is the power (watts = volts x amps) of the battery.