The new battery seems a lot better, no dramatic voltage loss, need to study it a bit more. The problem was not that I got stranded but more my own fear that it would happen sinceI spotted the rappid voltage drop.

Maybe I mentioned it already but the bad battery held voltage if not subject to any power drain.

The Ctek battery tester I have is this one:

https://www.amazon.com/CTEK-56-925-V.../dp/B00COPZ842