I took my 2012 W204 C300 4Matic to Valvoline instant oil change. Everything seemed fine on the drive home. After a couple of days, the car wouldn't respond to the keys and the battery seemed completely drained. We never had a problem before and previously the car could sit for weeks with no change in the battery charge level. After starting the car using a jump start battery pack several things are not working. The COMAND controls don't do anything. The seat belt warning doesn't make any sound.

First question, is it possible the oil change folks messed something up?

Second, is the electronic components/controls not working a common result of the battery dying? How can this be addressed?
Thanks,
Hish

Highly unlikely that your battery suddenly crapping out (which they tend to do) has anything to do with the oil change. When these batteries die, they die quickly (i.e., suddenly). This happened with my 2014 C350 a couple months ago.

Get a new battery and everything should be good. It may help to get a good scan tool and clear all the stored codes, but eventually everything should work normally.

Do yourself a big favor and get one of these: https://a.co/d/5cCbOkE