2015 BMX X1 sDrive Battery Only Charged up to 5V

Came back from a long vacation.

Car won't start - BMW X1, sDrive, 2015

- Battery Voltage was measured at the battery terminals - around 5V

- Jump started OK

- Battery Voltage was measured at the battery terminals - around 12.5V

- Kept car running for 6 hours inside the garage at night

- Shut off the car and measured the battery again - only around 5V

What could be wrong? Should try to disconnect the battery IBS?

Many thanks!

Alex