Aveo 2011 passenger airbag light on and electrical issues

Dear forum users, I have a chevrolet aveo 2011 and after a particularly large friend to take a trip in the passenger seat, the airbag light stayed on forever. Usually it would light up and turn off. I took to a mechanic and using a scanner it identified the error as B1620. We had to replace the battery shortly after as well, but the mechanic suggested replacing the whole aribag system which was very costly.
Reading a few posts here, I saw some people saying (after the battery was completely drained) that is possible to physically reset the airbag system as it might be thinking the airbag was deployed somehow. Any help is appreciated.

The clock is also unable to keep the time, so I'm wondering whether there's a short in the car somewhere. Again any help in troubleshooting would be very helpful.

All the best,