Great job done there (please do not forget to mark your last post here as solution)!
Also (IMO), there is no charging of battery going on after red LED light off (although around 0.9A shown, in range from 5.00V up to 5.30V relates to which power supply used there), yet repeating (up to your description) two or three times sudo systemctl poweroff and power on over power button (power supply still connected) will get your inserted battery to 100% (I’m quite sure, just follow when red LED light present, leave Librem 5 charging, either with OS showing 100% yet red LED light still … or when phone powered of). Thanks for your post as now I’m quite sure (as well) that actually repeated boot into this great Linux Kernel adjusts what you were into in this thread:
P.S. Your BPP-L503 battery cell (1S) is still fine (but you need to test my advice as above at first place, from time to time, monthly perhaps).