2005 Mazda 3. Replaced 3 batteries in 5 years, they don’t hold a charge. I am wondering about how to tell if I should be looking at a new alternator. As is I have to hook up to a battery charger everytime to start.
A few simple things can cause frequent battery changes. 1) Your drive to work is quite short, as are all the rest of your trips. - Kills the battery since it never gets fully recharged after a start. 2) Aftermarket stereos, amps, alarm systems, remote starters and other aftermarket devices are notorious for failures that drain the battery overnight. - Disconnect or replace them! and 3) An electrical short or bad sensor in one of Mazda’s computers is staying awake and drawing current when it shouldn’t. - This is a bit tough to find and may require professional help.
Can you do simple electrical tests? Do you own a digital voltmeter? (they are really cheap at Harbor Freight!)
The battery can be checked, for free, at most auto parts stores as can the alternator. Just drive the car in and they will test both. It will tell you if your battery is still good as well as the proper output voltage from the alternator (13.5-14.5 volts). The battery, overnight, with NO charger should be able to read 12.3 volts or more in the morning. If it is less than 12v, you either have a bad battery (you had it tested, right?) or you have something draining current from the battery overnight as I mentioned in #2 and #3. Time to take to a good auto repair shop and be prepared to pay for some diagnostic time.