Mercedes Repair Questions? Ask a Mechanic for Answers ASAP
Your vehicle still has the electric controlled hydraulic brake system so it is possible there is a malfunction with this system. This system is called Sensotronic Brake Control or SBC. The SBC hydraulic unit can detect faults such as hydraulic leaks, faulty pump, or even a bad brake switch. I suggest you get the system checked out at a dealership because if has anything to do with the SBC hydraulic unit itself, it will be covered under warranty. The SBC hydraulic unit/computer is covered for 10 years/150,000 miles. Smaller things like brake switches, brake calipers, or hydraulic lines are not covered.
I noticed you just replaced the battery, this fault may trip since the battery voltage may have been too low. I would suggest driving it a few more times to see if it clears by itself. If it doesn't, then the dealership can clear it and check to see if there are any actual faults.