What should you NOT rely on to assess the condition of a maintenance-free battery?

Relying on a built-in hydrometer to assess the condition of a maintenance-free battery is not advisable because maintenance-free batteries are designed to be sealed and do not have removable caps that allow for checking the electrolyte levels. A hydrometer functions by measuring the specific gravity of the electrolyte, which is only possible in batteries that allow access to the electrolyte. Maintenance-free batteries typically utilize absorbed glass mat (AGM) or gel technology, where the electrolyte is immobilized, making it impossible to accurately gauge the battery's state of charge or overall health using a hydrometer.

In contrast, methods such as using a digital multimeter, conducting a visual inspection for physical damage or corrosion, and performing load testing are effective ways to assess the health of a maintenance-free battery. A digital multimeter can provide voltage readings that indicate whether the battery is charged or needs replacement. Visual inspections can help identify signs of overheating or swelling. Load testing evaluates how well the battery can deliver power under a load, which is crucial for understanding its performance capacity.