my car battery has been replaced 2 times. My battery has be completely dead. on 2009 Volvo C70

I check lights ect. before leaving the car. The battery occurs spontanelsy. 3months sooner. It unpredictable. I have had it in the shop. They cannot find what the problem is. Please help me with this mystery.

Asked by for the 2009 Volvo C70
charge and load test battery if battery is ok then you have something draining the battery
My car does the same thing. What can possibly be draining it right window doesnt work and seat either could that be it
battery drains can be hard to find I would take it to a shop,I could tell you where to start but it is better you take it to an experienced tech