Resistors are used to limit voltage and/or current in a circuit and can have a fixed or variable resistance.  Variable resistors (often called potentiometers or rheostats) are used when dynamic control over the voltage/current in a circuit is needed, for example, in a light dimmer or volume control.

Resistance is opposition to the flow of current and is measured in ohms (Ω). An ohmmeter is used to measure the amount of resistance at a certain point in a circuit.

Connecting the 8 batteries in series multiplies their voltage while keeping their current the same yielding a 48V 5A configuration. Connecting the 8 batteries in parallel multiplies their current while keeping their voltage the same yieleding a 6V 40A configuration. Using a series-parallel connection, 4 batteries can be connected in series and 4 can be connected in parallel resulting in a 24V 20A configuration.

An inductor is coiled wire that stores electric energy in the form of magnetic energy and resists changes in the electric current flowing through it. If current is increasing, the inductor produces a voltage that slows the increase and, if current is decreasing, the magnetic energy in the coil opposes the decrease to keep the current flowing longer. In contrast to capacitors, inductors allow DC to pass easily but resist the flow of AC.

A diode allows current to pass easily in one direction and blocks current in the other direction. A zener diode is a diode which allows current to flow in one direction as normal and will also allow current flow in the reverse direction when the voltage is above a certain value. This value is called the breakdown voltage.