If your electric windows are playing up, try turning on your headlights and as much electrical equipment to see what happens, see if everything goes dim. If everything doesn't work properly, I'd say it's a battery connection. If you aren't getting good contact on the battery terminal, it can't conduct the full amount of current required, and the voltage actually drops throughout the car. If you look at the battery terminals and they are covered in crud, poor boiling water over the terminals, and it should get rid of that stuff.
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