Explanation: Emergency batteries are critical for powering essential GMDSS (Global Maritime Distress and Safety System) equipment during distress situations when the main power might fail. The specific gravity of a lead-acid battery directly indicates its state of charge and the health of its electrolyte. To ensure continuous operational readiness and compliance with maritime safety regulations, specifically those governing GMDSS installations, it is required to check the specific gravity of the emergency battery once daily while the vessel is in the open sea. This regular monitoring ensures that any issues with the battery's charge or condition are identified promptly, preventing potential failures during an emergency. Less frequent checks would not provide the necessary assurance for such a vital safety system.