‘02 Mazda Protegé LX Manual Why does my GOOD battery keep dying every few days?

What is your question?

Hello, Have had our 2002 Protege LX (5-speed) in the shop twice recently. Both times due to the battery failing after not running the car for about 3 days. Shop determined there is nothing wrong with the battery, the alternator, and they aren’t able to replicate the issue. They tell us the car is fine, no charge. ?? Other work done recently was 2 belts were replaced, otherwise she has always been super-reliable; it has under 60K original miles. There is an after-market security system installed, brand name is Cobra. It was installed about 16 years ago and hasn’t caused any Issues over the years. Could the Cobra be croaking? Lol Sounds like a good title for a song! :) Please advise; I missed my Dr. appt. this morning because the battery was dead. No struggle to turn over, nothing. I appreciate any and all feedback and ideas. I’m lined up to have a new battery installed on Friday out of desperation...but am not 100% certain that will fix my issue. Thank you! Megan

What makes this problem better or worse?

Better? Jump the battery. Worse? The car no being used for 3 days, then battery dies.

How long has your 2002 Mazda Protege had this problem?

A couple months.