I was not impressed with the Battery Percentages - though I didn’t dive into the data sheet.
Once I saw the graph of how steeply the battery voltage drops off at the end, I decided that the actual battery voltage would be much more accurate for my automation … and that the INA3221 lets me also monitor the solar panel’s output and USB-In power (when doing an emergency top-up in sustained wet weather).
Percentage seemed much more human-friendly … but I ended up making a gauge which I think does the job 
