In your response to the June 2021 Tech Talk question, you attributed the low voltage to bad batteries. Since voltage at the batteries was significantly higher than the voltage at the panel, could bad or undersized wiring be the source of the low voltage?
You bring a good point, low voltage at the DC panel can not only be caused by low battery voltage but also voltage drop because of undersized cabling, a bad connection between battery and DC panel. Good one! - Jeff