What prompted me to replace it was on a few occasions last summer the car - when very hot after a 'spirited' drive - had real trouble cranking over , just like you would expect to experience in only the coldest of mornings. The first time was after the car stood for about 10 minutes after re fuelling, it felt like I might need a jump start right there by the pump ! but she fired up.
This was not excessive cranking al la CPS fault as I had already replaced the CPS a few weeks before, but very slow ,flat battery style cranking.
The C55 AMG holds a LOT of heat under the bonnet and that got me thinking , this was the first time for me that any vehicle I have driven or ridden had trouble cranking over when hot. A quick search on the internet promoted me to change the battery.
A battery that had never hinted that it would ever let me down in the very coldest of conditions ...but might fail me when hot.
As soon as the new battery went in the 'fault' went away.
I remember when you posted about that originally. A very strange issue as a battery's internal resistance normally drops as temperature rises, and voltage increases! I can't think of a logical explanation (but I'm not doubting what happened!).