1990 300E Battery/Alternator issue

[NeralPal]

Ok, so my car randomly started dieng one day while I was driving. I had it towed to the local dealership and they couldnt find anything wrong with it and they couldnt get it to die out. So I drove it for another week and it started dieng again. The engine doesnt go out unless the card completely stops, but all the electrical parts in the car fizzle out. (radio, Dash lights, etc) Now the only way I can start the car is by a jump. The battery is really old but alot of people have told me its the alternator. Anyone have any insight on this issue? I would appreciate any input.

Thanks,
Neralpal