2002 C240 Mercedes Check Engine Light Problems!!!!!

[BigRed0803]

I purchased a 2002 C240 a few months ago. I bought the car from an individual, the car was in great shape it only had 75k miles on it. I purchased the car with the check engine light on, which has turned out to be a challenge. I took my code reader with me and saw that the CEL was Cylinder 4 misfire, I thougtht no big deal. When I drove the car home it seemed somewhat underpowered, so I changed all the spark plugs and the checked all the wires, which were all ok and that seemed to fix the problem. Around a month later the CEL popped back on and it was again Cylinder 4 misfire. I went ahead adn changed the coil and both plugs and plug wires for that cylinder to take car of the problem and not take any chances. Again all was good for around a couple weeks. Then the same has happened again. CEL on and Cylinder 4 misfire is the code, but this time in the display it said battery/alternator visit workshop, could this be tied in together? What else could be the issue for this one particular cylinder, am I thinking right that if it was a CAT converter problem it would throw the misfires for every cylinder on which ever side was bad? It runs really bad when the light comes on, I thought about the MAF, but I thought it threw a particular code not a cylinder misfire code. Any ideas? The last time I changed the plugs on cylinder 4 they had a lot of gas on them, making me think it may be a bad injector.