Like fuses, circuit breakers stop current flow once it reaches a certain amount. They have the advantage of being reusable (fuses must be replaced when "blown") but respond more slowly to current surges and are more expensive than fuses.

Voltage (V) is the electrical potential difference between two points. A voltmeter is used to measure the voltage between two points in a circuit.

The transistor is the foundation of modern electronic devices. It is made entirely from semiconductor material (making it a solid state device) and can serve many different functions in a circuit including acting as a switch, amplifier, or current regulator. A transistor works by allowing a small amount of current applied at the base to control general current flow from collector to emitter through the transistor.

Capacitors store electricity and are used in circuits as temporary batteries. Capacitors are charged by DC current (AC current passes through a capacitor) and that stored charge can later be dissipated into the circuit as needed. Capacitors are often used to maintain power within a system when it is disconnected from its primary power source or to smooth out or filter voltage within a circuit.

Connecting the 6 batteries in series multiplies their voltage while keeping their current the same yielding a 72V 20A configuration. Connecting the 6 batteries in parallel multiplies their current while keeping their voltage the same yieleding a 12V 120A configuration. Using a series-parallel connection, 3 batteries can be connected in series and 3 can be connected in parallel resulting in a 36V 60A configuration.