What is the correct action when the battery fluid level is low?

When the battery fluid level is low, the appropriate action is to add distilled water. Lead-acid batteries operate using a mixture of sulfuric acid and water, and maintaining the correct fluid level is crucial for the battery's performance and longevity. Adding distilled water helps to restore the electrolyte level, ensuring that the chemical reactions within the battery can occur effectively. It’s important to use distilled water rather than tap water, as tap water can contain minerals and impurities that may harm the battery's components.

The other options do not address the immediate need to replenish the fluid level. Replacing the battery is unnecessary unless the battery is malfunctioning beyond just low fluid. Charging the battery is only relevant if the battery is not holding a charge, regardless of the fluid level. Cleaning the terminals is a good maintenance practice but does not resolve the issue of low fluid, which could lead to battery failure if not addressed promptly.