Hello
Does anyone know if the coding in the current MB keys is volatile?
i.e. can I just replace the battery myself without losing the coding, and if
so how?

Having written that I bet its in the manual, but maybe someone has some
experience of doing it.
I have never needed to do it as I don't keep the cars long enough but my SLK
has the remote operation of the roof from the key  which is bound to
accellerate the battery drain by a lot as you have to hold it down for 20
seconds.
Or maybe it doesn't ?