well... I don't have a deisel engine but, here's what I have done over the past winter when the battery would drain on the 190e: Don't remove battery terminals, hook batt tender cable up to + terminal then hook - up to engine block. Then plug in charger. Usually I'd set it on high for just a minute or two then unplug the beast take off the leads to batt/engine and try to fire it up. Never took too long hasn't had any deleterious effect on the car so far, but don't know about the diesel question you posed.
1985 190e 2.3