Batteries act like water tanks. Water tanks are placed on towers or on top of hills to increase water pressure, allowing water to flow. And batteries use electrochemistry to create a voltage, allowing electrical current to flow through a circuit. In our kits, batteries are stored within battery boxes like the one shown above.
Batteries have a positive and negative side. On this battery box, the black wire is negative and the red wire is positive. The positive wire connects to power, the highest voltage part of the circuit. The negative wire connects to ground, the lowest voltage part of the circuit.
Current flows from the positive side of the battery through the circuit and back through the negative side. Current then flows into the battery. As it travels through the battery, the current is boosted and picks up voltage. With voltage renewed, the current has the power to flow into the circuit again. This is why a circuit is called a "circuit", for the circular path current takes over and over again.