I have a 08 Mazda 3, 2.0 engine. I replaced the battery a couple of months ago. The other morning I went out to start the car and the battery was dead. I jumped it off, let it run for a bit and then drove it a little bit. The next morning, the battery was dead again, then I noticed that the map light had been left on, so I jumped it and let it run. Next day, dead. Yesterday I jumped it off and was going to run it up to Advance and have them check the battery. I got about 500 ft up the road and it died, no power at all. Got back to the house, took my multi meter and checked, less than 2 volts. I jumped it again, checked it with my meter while running to check if it was charging, I was getting good charging voltage, about 14.2 Volts. I then turned on the lights, wipers, radio, and flashers, and the charging would fluctuate between 14 and drop to about 6. I also disconnected the positive cable while it was running and it continued to run. I then put the battery on a charger to get it fully charged and checked it again and got 14.2 volts with all the lights and stuff on again, so apparently the alternator is fine. Anybody have any ideas, I guess its possible I got a bad battery, or maybe I'm just missing something.

 

More than likely the battery is toast.