You just look at The voltage to ground across the battery, and the voltage at the fuse box to a good ground on the engine. No need for long cables. If you are worried about the ground cable, remove it and measure resistance on it directly. You can use a temperature gun to see if it gets warmer due t...

I'll make the measurement and snap some pix

It does,t matter if the small lights on as long as they are on for both measurements.

Captions to follow. Ambient temp 1.0 C

You really have 2 symptoms and they should be troubleshooted separately. They could be related, but there is a fair chance that they are not. One is your parasitic draw issue. That one didn’t make your car break down in traffic. I ignored this symptom in my post above as it is the least of your issu...