Final answer:
The minimum voltage required during battery tests varies by battery type, but battery testers operate by drawing current through a load resistor to assess if the terminal voltage drops below a set threshold, indicating high internal resistance and a weak battery.
Step-by-step explanation:
The minimum voltage required when performing battery checks using battery testers depends on the specific type of battery being tested. However, battery testers like those depicted in Figure 10.9 and Figure 21.13 work by applying a small load to the battery using a load resistor to intentionally draw current. This process helps to reveal whether the terminal voltage falls below an acceptable level, which would indicate a high internal resistance and thus a weak battery. The exact minimum voltage can vary but is dictated by the standards for each type of battery.
For instance, a standard 12-volt car battery is often considered discharged if it is at or below 11.7 volts when tested. Battery testers really test for the internal resistance of a battery—if internal resistance is high, the battery will display a low terminal voltage under load conditions. Remember, the voltage across the battery must be equal to the total voltage across all other circuit components that are in series with the load resistor.