Aux battery malfunction/steering problems 2010 Mercedes E350

This morning when I started my car I got an Auxilary Battery malfunction message on the dash. I drove for about 15 min parked drove again about 20 min then parked and then drove for about 5 min when I noticed a smell and my car heat not blowing (it’s 2 degrees out). Car became almost impossible to steer but engine was still running and I got a huge Red battery error message on the dash I tried shutting the car off and restarting it but same problem persisted. Do I just need to replace my auxilary battery or is there a larger problem? Thanks please help!