Mercedes Benz 2002 C240

I have a MB 2002 C240 that is about 5800 miles overdue for a Service B. Back in Oct when my car started flashing the service notification, I called the dealership and they told me that Service B is an oil change and 21 point check; for $500. I've regularly gotten the Service A and Bs done since I bought the car preowned 5 years ago, but this was the first time I asked what was actually involved and I was turned off by the exhorbitant fee for a simple oil change. Since then, I have had about 3 oil changes at a Meineke in my area, where I asked that they use the Mobil 1 oil that the dealership said should be used. Around the same time that the service notification started flashing, my car began to shake when idle. Again I took it to the Meineke and they said two of my tires were worn and the alignment was off and that this may be causing the shaking, so I got that fixed. But the car was still shaking. This month, I had to replace my car battery, as another notification flashed (only once) saying I should check my battery/alternator. I had it replaced at the Meineke after calling the dealership and being told that it was fine to take something like that to a local place and not the dealership. Meineke said it was the battery and not the alternator. About two weeks later, I received the battery/alternator notification again (once). I'm not sure what is going on with my car-- is there a malfunction with the CPU that it's giving me the battery/alternator notification even though the battery was changed? Is it possible that Meineke didn't change the battery and just charged me for it? And no one can figure out why my car is shaking. Please help!