Which feature is essential for the maintenance of a survey meter according to the Nuclear Regulatory Commission?

The essential feature for the maintenance of a survey meter, according to the Nuclear Regulatory Commission, is the capability for a battery check. This feature is critical because survey meters rely on batteries to function properly, and ensuring that the batteries are in good condition is vital for the accuracy and reliability of radiation measurements. Regular battery checks help prevent possible failures during use, which could lead to inaccurate readings or complete device inoperability in situations where radiation monitoring is crucial.

A feature like operating without a battery may be useful in specific contexts, but it does not address the routine maintenance needed to ensure the device's daily operational readiness. Similarly, while emergency shut-off mechanisms and digital displays are valuable for safety and usability, they do not directly pertain to the ongoing maintenance and reliability of the device as strongly as a robust battery check process does.