What's causing my car battery to discharge?

Youve got a bad battery , or a short in the battery, maybe the battery is low on water , if its that type , or a wire is lose, on the starter pulling the power away,

Check the wires to the starter. do you have an aftermarket stereo if so some of them have security that pulls juice you can disconnect the security on the stereo on the back

Corroded battery terminal connectors can also be a cause. Remove the connectors, clean inside with a file, knife or sandpaper and then around the terminals. If that doesn't solve the problem then look elsewhere.

I also have a buick park avenue and had the same problem had it in the shop and had every test done to it they couldnt seem to find out what the problem was had the battery tested and altenator..said they were both fine. but..the alterator was bad...there is a regulator in it that when it gets hot it drags... anyway i decided to go ahead and spend the 150 bucks for the alternator...and try it its been almost 2 weeks and my car has been starting just fine.......Hope this helps you...

Any good auto parts will check your battery for you especially if batt is over 2 years old the internal plates can crack or wear out and will hold a partial charge for a few daws or less ==check all the obvious such as add on equipt over head or floor lighting [ if windows are tinted you wont notice them eaisly] check hood and trunk lights they operate on mecury s/w and only turn off when you close them====if you cant get to an auto parts a simple test if youhave time disconnect batt for a few days if it is weak or dead then you need a new one