Final answer:
The question is about the testing intervals for water-activated batteries in Emergency Locator Transmitters. Regulations for these testing intervals can vary by country and governing body. Without a specific reference to a regulation, an exact answer cannot be provided.
Step-by-step explanation:
The question asks about the required testing intervals for Emergency Locator Transmitters (ELTs) that are powered by water-activated batteries. ELTs are emergency beacons that broadcast a signal to notify search and rescue services in the event of an aircraft accident. Although the question doesn't specify the regulatory agency, in the context of aviation safety, regulations can differ by country and organization. For instance, the Federal Aviation Administration (FAA) in the United States has certain requirements for the periodic testing and replacement of ELTs and associated batteries. However, without a specific reference to a regulatory body or standard, providing an accurate answer regarding the testing interval is not possible. The general concept would be to follow specific aviation regulation guidelines, which may mandate the testing of batteries every few years to ensure functionality.