Date registered: Sep 2006
Vehicle: 2004 CLK 240 Coupe
Location: Norfolk. UK
Mentioned: 9 Post(s)
Quoted: 343 Post(s)
Your battery might be flat - but not dead.
In other words, you should be able to re-charge it - without removing it from the car, if you have power sockets in your garage. First check the electrolyte level in all 6 cells, and add clean distilled water if required. The alarm will not buzz while charging.
It should easily have survived a break of 5 months, although there is a constant small drain on the battery even when the ignition key is out. Clock, various memories, alarm circuit, etc.
My 2004 CLK still has the factory-fitted battery, and it is in fine condition.