Where is battery voltage indicated in an aircraft?

The correct choice is the electrical and summary synoptic page, as this page is specifically designed to provide an overview of the aircraft's electrical systems, including battery voltage. It presents critical information related to the status of electrical power sources, allowing pilots to quickly assess the health of the battery and overall electrical system.

This synoptic page typically consolidates information from various systems and displays it in a clear and accessible manner, which is essential for effective monitoring during flight operations. While other options may display various flight-critical data, they are not specifically dedicated to providing real-time electrical system monitoring or detailed battery voltage information. Thus, the electrical and summary synoptic page serves as the primary and most reliable source for this information in an aircraft.