Who is correct regarding maintenance-free batteries having a built-in hydrometer and testing methods?

Maintenance-free batteries are designed to minimize the need for regular servicing and maintenance by the vehicle owner. Unlike traditional batteries, which require periodic checks of electrolyte levels and sometimes involve manual testing with hydrometers, maintenance-free batteries typically include sealed, factory-filled electrolyte and are not designed for such maintenance.

In the context of hydrometers, these devices measure the specific gravity of the battery's electrolyte solution, which is useful for assessing the battery's state of charge and health. However, maintenance-free batteries do not have a hydrometer built into them. Instead, they are constructed to be low-maintenance or maintenance-free, meaning that they do not provide an easy way to check their internal condition using a hydrometer.

Both technicians in the scenario provided incorrect assertions about the presence of hydrometers and the methods for testing maintenance-free batteries. Therefore, the answer indicates that neither technician is correct, as maintenance-free batteries lack hydrometers and do not follow the conventional testing methods associated with traditional lead-acid batteries.