In a series circuit, the battery is used to provide a source of electrical energy to power the circuit. The battery supplies a constant voltage to the circuit which is necessary for the electrical components in the circuit to function properly. As the current passes through each component in the circuit, the voltage is distributed among them, which affects the brightness of the lights or the power of the device. Without the battery, the circuit would not have any source of electrical energy and would not be able to function.
