Hi! Can I weld a muffler while attached to the hybrid car without damaging the Hybrid Batteries?
Thank you so much!

 

That's a problem on any vehicle. As long as your grounding point is good and close to your welding, no but you have to make that your good is good.

You really should disconnect the Hybrid battery pack and the 12V battery to be safe. There may be a reason that not needed but only somebody who knows the electrical system like the back of their hand can answer.

I had a friend fry the electrical system on his farm tractor like that.