Final answer:
Three types of voltage indicators/testers include heavy-duty battery testers for large batteries, digital battery testers for small batteries, and voltmeters/multimeters for various electrical measurements. All these devices assess a battery's condition by checking terminal voltage or internal resistance.
Step-by-step explanation:
The three types of voltage indicators/testers discussed are: heavy-duty battery testers used for large batteries, compact digital battery testers for small batteries, and multimeters or voltmeters. Heavy-duty testers, like the one used on the USS Nimitz, have small resistances capable of dissipating high power amounts, which makes them suitable for substantial battery systems. Compact battery testers provide a digital reading to indicate if the terminal voltage is acceptable for small batteries. Lastly, multimeters or voltmeters measure the potential difference between two points of an electric circuit, serving as a versatile tool in electrical measurements.
Battery testers use load resistors to intentionally draw current for assessing the terminal voltage and hence the battery's internal resistance. High internal resistance signifies a weak battery with a low terminal voltage. Earlier devices like galvanometers paved the way for modern multimeters, which became portable with advances in electronics such as printed circuits and transistors.