Does the mppt controller talk to the
battery monitor over bluetooth? I have two 75/15 MPPT controllers running in parallel, and I notice that they do tend to report funky things so I put more faith in the actual amperes flowing,
history graphs showing total charge input and, of course,
battery SOC. I guess you should double check your battery chemistry setting at the controller just in case this isn't matching your
batteries.
I had a problem with a Victron battery management gauge not powering at all during the week. The issue was minor
corrosion on the fuse connecting the shunt to the positive battery supply. A quick clean and all good. Had exactly the same thing happen to the
GPS the next day, too. This isn't an uncommon problem around my way this time of year. It may not relate to your issue, but I reckon there's a high resistance in the circuit to the gauge (which I'm guessing reads voltage at the gauge itself rather than the shunt). Give the circuit an
inspection and clean with
electrical contact cleaner and see if it changes. I use silicon grease to help protect contacts from further
corrosion.