Welcome! Sounds like you may have an electrical draw ,that drains the battery when it sits idle. I am assuming it charges ok while running. Pull off 1 battery terminal, + reinstall it while looking for a spark, when touched to battery post. If it sparks, you have a draw. If so, go to the fuse panel, + remove the 1st fuse. check again for spark at battery, repeat as necessary until no spark. That will tell you which circuit has the problem. consult a wiring diagram for your car, and proceed to check for bare wires ,pinched wires, places that the insulation has been worn off, and areas that could be touching metal. Also , clean all ground connections, and fuse connectors. This is a little time consuming, but you won't be paying a shop to do the same process. Goodluck !