Hi,

I have Chevy Malibu 2002 model. The car battery is getting drained overnight. I have shown to mechanic but he could not fix the problem. I had already spent 600$ but the issue is still not fixed. He has replcaed the hood switch as well as ignition switch but still battery is getting discharged.

 

You should take it to a better mechanic. One that knows how to properly check for a draw

 

Don't for get to check some things for yourself, check to make sure the glove box light is not staying on if you have one, unplug any accessories that you may have added, remove any chargers from the cigarette lighter(s).
Take a walk around your vehicle in the evening when its dark and check for any lights on.
Its a little tedious but you can try removing 1 or 2 fuses at a time in the evening, leaving them out over night to help identify the possible circuits that are causing the drain.(putting them back in the morning and if vehicle starts you know what fuses were pulled and what circuits were causing the drain)

just some suggestions that require no deep tech know-how or tools