What are the battery requirements for the SK-5207, and how does the panel indicate a low-battery trouble?

The SK-5207 requires two 12 VDC batteries of the same ampere-hour (AH) rating, connected in series using the two sets of battery leads provided by the 5198 power supply (Page 20) [11].

To connect them, attach the first set of red and black leads to the positive and negative terminals of the first battery, then repeat with the second set of leads for the second battery (Page 20) [11].

I couldn't find the specific low-battery indication method for the SK-5207 in the provided manuals, though the panel is noted as the main source of trouble annunciation (Page 20) [11].