What is wrong with my car? Maybe the battery or alternator?

[needshelpt]

Ok, so the best way I can explain this is to tell the story.

So, the little battery light on the dashboard of my car turned on...and a day or two later the car just turned off on me. So, I went and bought a new battery and it's been fine. Then while driving, the battery light would flicker on and off, so I just kinda ignored it...until it happened again! The car turned off and would not turn on. This is with the new battery in place. My dad came to my rescue with a replacement battery and the car started up. What happened?! The battery was new!

If anybody knows...can you tell me what's wrong, and what I need to buy or how much it would cost to get fixed? thanks!
It broke down on me the second time while using the new battery for the second day in a row. Also, to add to the details...before it turns off, the power goes down. First, the radio turns off...then the lights dim all over the car...and it feels like the car is struggling to stay alive.

So, what am i supposed to do now? What do I do with my $110 battery i got from AutoZone? Can I get my money back somehow? Did I burn it due to faulty alternator/wiring?
it's a 1992 Mercedes Benz 300SE

 

[RonE]

You most likely have a bad alternator, these are the classic symptoms. You can test this if you have a voltmeter. With the car running put the leads of the voltmeter on the battery terminals. You should get around 13.5 and 14 volts. If you don't have a voltmeter go to a shop they will have one. You don't say what type of care but replacements will run around $75 to $150 for a rebuilt one and about twice as much for a new one.