Given the COVID-19 crisis, our cars have not been driven much. The XC60 sat for about a week, then started right up. But when I got to the first destination and tried to open the hatch, it just clicked and a notification something like Low Charge appeared. I was able to help it open and it has been OK since. I saw the Low Charge message again a few times, but it always started right up. Later, I did some voltage measurements:
Time. Main Battery. Aux. Battery
1:22PM. 12.59 12.66 Engine off
1:25PM. 15.28 13.15 Engine Idling for 3 minutes
1:45PM. 12.25 12.72 Engine off
3:20PM. 12.25 12.64 Engine still off
Then I did a resistive load test and it measured 400CCA, in the green, then the main battery returned to 12.37 Volts.
Since then, a few days later, everything seems normal, except that start/stop no longer works. Under the My Car menu, Start/Stop gives a message: "At the moment the electrical system does not allow use of the Start/Stop Function. The following examples may be reasons for this: the battery is charging or the battery temperature is too low."
The batteries are original, but AGM should last longer that wet batteries, right? Any advice will be appreciated.
At 72 K miles, it is beyond the original warranty, but I have the Steingold extended one. Will that cover having the battery monitor reset if that's all it needs?