I have had an ongoing problem for 2 years with my 2018 Kodiaq .2.0l TSI battery losing charge over a few days and the battery charging randomly at different charge rates.

To date I have had:

2 replacement batteries (at my cost)

then under Extended Warranty (now expired)

1 replacement negative battery lead (with sensor)

1 replacement alternator

Symptoms (monitored with Ancel Battery Manager device and multimeter)

Battery discharges in a few hours from 100% SoC /12.8v to around 65% then continues slowly after that over several days

Charging when driving starts at 14.3v but even when battery is low quickly drops and does not get to full charge even after half an hour of driving

Static current too high warning now showing on ODBII monitor but dealer had the car for a week and did not find any fault

Also shows "DAB aerial short circuit to earth" warning

I need to gather more evidence to persuade dealer to pursue. All suggestion welcome!

A friend has a new Kodiaq VRS petrol with identical symptoms. Is this a known issue?

It sounds as if you may have a parasitic drain issue, is your infotainment system original?

Can be a bit of a lengthy process of elimination to find which module is not going into sleep mode.

The voltage variation you mention is normal - the smart alternator is designed to do this to allow for energy recuperation under deceleration and/or braking.