third battery in two years...they won't hold charge on 2008 Mazda CX-7

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dealer says he can't find any problem that would cause battery drain.This is the third battery in two years...all Mazda approved...If the car was not used for 2 or three days,dealer says that is the problem.If the battery died while I was at work, they say I don't drive long enough distances each day to keep battery charged.After driving 125 miles trip,car was not used for several days and battery died.They said it sat too long without being used
(1) Answer
Discharge to charge rates (almost 5 to 1!) can be the problem- if this is a consistant short trip vehicle. However, it sounds like you have a parasitic drain on the battery that needs to be found. Find a reputable shop (other than your dealer) that will take the time (and it make take some time) to find the draw down.