What action must be taken if battery power is below the minimum on either EFB?

In this situation, ensuring that necessary resources are available for flight operations is critical. If battery power on either Electronic Flight Bag (EFB) is below the minimum threshold, the most prudent action is to print paper approach charts before flight. This ensures that all essential navigation and approach information is available in physical format, thus safeguarding against potential reliance on electronic devices that may become inoperable due to insufficient battery power.

The other options do not fully address the immediate need for securing flight safety and operational readiness. Though a full system check can be important for various scenarios, it does not directly mitigate the risks posed by low battery levels on the EFBs. Calibrating the EFB units is more relevant for ensuring accuracy and performance, rather than addressing power-related concerns. Rebooting aircraft systems may be useful in certain operational circumstances, but it does not resolve the issue of inadequate battery power on the EFBs and may not restore power or functionality in an effective manner. Thus, printing paper charts provides a tangible safeguard in managing the risks associated with low battery levels.