My (VW Polo SE TSI Mk5, 2015, 1.2, bought secondhand) car just had a new battery fitted (EFB for start-stop cars) and on checking the battery voltage with a multimeter at idle (engine on, car stationary) it comes up to about 13.1, occasionally 13.2. Revving the car bumps it up a bit. I worry if I don't have an issue with the alternator, as reading up on it online it says at idle it should be about 13.5, so wondering if the alternator is struggling to charge it.
Is there a canonical reference for my type of car as to what the voltage should be in these circumstances? Anything else I can do to settle the issue of whether there is a problem with the alternator?
Edit: Could the lower voltage on the new battery be down to the fact that I might have a smart alternator and since the battery is new, it doesn't drive as high a voltage as it would on an older battery?