Audi A4 2lt TDI 2008 not starting in the morning

For the past couple of weeks my car has been taking a slight bit longer to
start in the mornings.  I wrote this off to colder mornings.  This car is normally
parked in a garage but I left it outside last night.  This morning the car just
didn't want to start.  Seemed like classic battery issues, it cranked half way
on the first attempt and after a couple more tries nothing happened.  The
lights were still on and the radio played, but I couldn't even get the electronic
hand brake to release.  Seemed like the power dipped every every time I
tried to release the handbrake.  

I connected my jumper cables to my other car and had it idle for about 5
minutes. Afterwards the Audi started perfectly on the first go.  I drove it for
about 30 minutes to the nearest battery center.  They tested the battery and
the report showed that the battery was still 100% (I bought the battery in
November 2020, so it is still fairly new).  They checked to confirm that the
battery is the correct size for the car.

From there the car started fine on its own and it is running perfectly.  

This doesn't seem like a started problem, as the electronic hand brake
should not be impacted by the started.

Any ideas what could be the cause of this problem?

Thanks