Battery keeps draining and charges well.
Is there an easy way to determine if alternator is functional??
Also, could it be voltage regulator?? How do I know??
(1992 500SEL)

Does the battery also discharge when it is disconnected from the car for a period of time? If so, then the battery has an internal short. If not, it sounds like you have a current draw somewhere. There is lots of stuff on this in the archives.