Mazda Repair: New Miata battery will not hold a charge, miata battery, duralast gold

Question
I have a 1992 Miata and I have replaced the battery three times in one year with the same brand, a Duralast Gold.  Unless I run the car on the freeway daily the vehicle needs to be jump started.  I have taken it to my mechanic twice and he cannot find the problem.  He says he ran draw tests and has tested the alternator but he does not know what it is.  Can you please help, thanks!

Answer
you machanic is in the right place looking for voltage draw and tseting the alternator did you by chance also make sure the starting system wasn't drawing to much power. i'm not sure if those have built in voltage regulators or not but that's also something to check. either that or the battery supplier is giving you out batteries meaning they've been shelved for longer then they should be and aren't preforming properly

other then what you tect has done and those other suggestions that's all i can think of