I have a 2005 Mercedes Benz C240 AWD.
The vehicle sat for two days. When starting this morning the car struggled a bit but started. (Brand new battery installed 1 year ago) (bosch pepboys battery)
There was a strange fuel smell/emissions exhaust death smell from the exhaust, smell did not come from under the hood as I popped the hood immediately.
I drove it around, smell went away.
Handed the car over to the wife so she can go shopping.
When she parked the car she videoed a crazy clicking noise coming from under the hood. Keep in the mind the car was shut-off.
She also told me the fog lights below were blinking while this crazy noise was going on. I have no idea what this could. Anyone out there ever experience this? Thanks

 

hit the Alarm button on your remote key and see if the alarm goes off.. if the alarm siren horn cannot be heard and the only thing happening is the fog lamps flashing, you probably have a dead or internally shorted alarm siren causing the issue.. obviously this is just a guess because it difficult diagnosing electrical issues over the phone or internet, but its a starting point

 

BTW that Bosch battery sold at Pepboys does not meet the amp/hour requirements of your model. You need one with at least 100 ah rating. The reason for this high rating is that these cars even when locked and parked have a lot of things quietly running, and one of the obvious symptoms of an insufficient battery is electrical gremlins that show up after the car sits for a while.

 

When purchasing the battery I made sure I replaced the original battery with the same specifications.
There is a possibility that the battery, although close to $300, is not as strong as the German silver bodied battery that was in there prior.