Which of the following is NOT a requirement for a control panel?

The requirement for a control panel in a septic system typically includes several critical components to ensure proper operation and safety. A backup battery, while beneficial for maintaining system functionality during power outages, is not universally mandated for all control panels. Its inclusion may depend on the specific design or requirements of the system rather than being a standard requirement.

On the other hand, the HOA (Hand-Off-Automatic) switch allows for manual control of the system, the event counter tracks operational data or counts system cycles, and overload protection is essential for safeguarding against electrical issues that could damage system components. These elements are generally important for the performance, monitoring, and safety of the septic system, making them standard requirements in most scenarios. Thus, it is the backup battery that stands out as not being a fundamental requirement for all control panels.