Originally Posted by CapeX5

Don't trust the battery light being on or not. I had one that had a bad alternator, but the light did not come on. And the bulb was good. Never figured out why.
OP, if you don't know how to use a multimeter, than take it to a competent garage. First you need to have a fully charged battery. Whether that is your existing or a new one. Once you have that, and the car is running, one can diagnose whether the alternator is charging the battery. DON"T just go replacing parts without correct diagnoses.
And, on the window switch, just a get the whole unit, not individual. There are all kinds of electronics in that thing that you don't want to mess with if you try to dissassemble it. They are cheap and used on E39's as well. Get the battery/charging issue resolved than do the switch. You don't need to take the door panel off either.