AgentR

Hi, I bought my '16 A3 e-tron SB a year ago here in Norway, and I have really liked the car, but I have had one strange issue that I have been wondering about since the start.

I do not have a charge option where I live, so I have to charge at charge-points when I have the ability to do so.
On some days, the car has drained alot of the high-voltage (driving) battery over night. Sometimes removing as much as 50% of the full charge in one night.
It seemed to be more prevalent on cold nights, but there was no consistency to when it would or would not happen.
In addition I sometimes get a warning message that the 12v battery voltage is low, and that charging will be performed while driving. (I can take a screenshot if anyone wants to see that)

I have a Comma Two self-driving device that I have hooked up to my car, and I figured I could use that to log the charge of the 12v battery, since it has an API to get that data from the car. (It connects to my house WiFi)
So the last couple of days, I logged the battery voltage every half hour, and what I found was very interesting... This night the "phantom drainage" happened again, and I have some evidence this time.
My car was parked up until the first spike at around 04-28 13 (1pm), and then parked again until the morning after around 7am. No charging cable was plugged in.
The car has been actively topping up the 12v battery during the whole night, and I do not see why, since is seems the voltage never dipped below 12v. (Which should be normal)
Does anyone know why this would happen, or have any insight into why the car would do this?
Image of battery statistics attached

wmtunate

Nominal voltage for a lead acid "12 V" battery is actually closer to 13.8 V. 12 V is actually too low, so that's why it's being topped up. You probably have a bad battery, especially if it's original. 5-6 years is about the average lifespan.