Final answer:
Battery testers check terminal voltage by applying a load, revealing internal resistance levels. Large batteries use testers capable of high power dissipation, whereas small batteries use testers with digital displays to indicate voltage levels.
Step-by-step explanation:
To check the battery voltage and the charging system, battery testers are used which apply a load to the battery and measure the terminal voltage. These testers have small load resistors that intentionally draw current from the battery. The purpose of this is to determine if the terminal voltage drops below an acceptable level, which would indicate high internal resistance and thus a weak battery.
Battery testers are particularly useful in ensuring the proper functioning of a battery's internal components. For large batteries, such as those on the USS Nimitz, a tester with the capability to dissipate large amounts of power due to its small resistance is used. Conversely, for small batteries, a tester with a digital display can show whether the terminal voltage is within an acceptable range.
The principle behind this testing is that the voltage across the battery needs to be equal to the total voltage across all other circuit components that are in series with the load resistor.