My battery is not staying charged overnight. About a month ago the car lost all battery power in our driveway. At that time we had the battery and the alternator replaced. After two weeks we had the same problem. The problem this time was the battery cables had internally coroded so we had those replaced. We took the car home again, but the battery died again! They replaced the battery but the next night the same thing happened. We have checked each night to make sure nothing has been left on that could drain the battery. What is making the battery lose power so quickly like this?

i would start by making sure your alt is charging at above 13.5v then see here:
https://www.gmforum.com/trouble-shooting-test-procedures-141/amp-draw-test-293647/

To pinpoint your parasitic draw on your batt definitely see that link.

Just a guess here, but if your car has Dyna-Ride, my guess is there is a leak in one of the bags that hold pressure, if so the system will come on frequently too re-pressurize, the system works even when the car is shut off.
Mine is bad on my 96' Park Ave, I have a small leak, and that causes it to kill my battery overnight, it has gotten to the point that until I can address the issue I just unplug the negative battery cable when not driving it, I may had a battery quick disconnect until I can afford to fix the issue.

Hopefully you find out your issue is something cheaper to fix, I'll probably go with some regular struts, and disconnect what controls the sensor for the Dyna-Ride system.

Sorry for the typos in there, unfortunately I do not see a way to edit my post to fix them. :/