Replacing E320 coupe battery (constant mains charge required?)
 

I have recently bought a 1996 MB E320 and need to replace the battery. This may seem like an odd question, but I have been told by a mechanic (admittedly, not an auto-electrician) that when changing the battery on these cars (with alarm and immobiliser) a constant charge should be fed to the terminals via a separate mains power source so as to avoid having a period of "zero power" in the system. "Downtime" has been known to cause problems with the ECU etc (apparently).

I am puzzled. Has anyone else heard of this, or should my mechanic go back to school?!?

I replaced the battery in our 1998 E320 without taking any special precautions ... merely disconnected the old battery, removed it, set the new one in place and connected it. Never needed to reset the radio code. I would check your Owner's Manual for any warnings or specific recommmendations.

When I replaced the battery in our C-Class, I kept 12V to the battery leads with a couple of wires/alligator clips. I believe that the radio would have lost its code and pre-sets without this.

Worked fine.