At what low voltage threshold would W210 key not turn?
 

This question arises out of a separate thread....but I thought the question can stand on its own merits and thus warrant a new thread.

According to my indie, the electronic ignition on the W210 requires a certain voltage for the handshake to occur and the key to turn. Does anyone know approximately what this voltage might be?

Does a low voltage physically stop the key from turning?

nope

According to my indie (who's a first rate MB mechanic), yes. Here's what he said: "it could be the relay or something as simple as a dirty battery cable but remember if the volt[age] is low in the system the key wont turn."

I have noticed that at 12.5V standing voltage the release handshake is very slightly delayed.. I have also come to know of another persons experience that below 12.1V standing voltage the system wont work.

Same person first told me of the cold and EIS problem too.

his recommendation is to keep the battery in top shape.