Battery charging voltage on a non intelligent panel (which I assume this is) should be 13.69 - 13.75 v assuming normal ambient temp.
Check charge current and charge voltage on load. Best way to test this is with a partially discharged battery and again when fully charged.
I'd be concerned if load reading was below 13v and below 13.5 ish when fully charged
An intelligent charge panel will ramp up voltage depending on charge state so harder to test