Hi, I own a Mazda CX-7 2011 iSport and I currently sit at 123,500 miles and just yesterday my batterly light came on when I was driving 33 minutes back home. The car recently had its battery replaced 5 months ago as well as the alternator 5 months ago so they're both brand new and under warranty. I hooked up my multimeter and measured the battery before I had it replaced again and it read at 12.07 volts DC. When the car started the battery voltage dropped to 11.8 Volts and on my drive to work, which is 11 minutes away, it died on my job place's parking lot tripping the check engine on the control module since the battery died. Autozone ended up replacing my battery for free and the check engine code went away, however not too long after my drive back home the battery light came back on. My terminals are not corroded and like I said the alternator is brand new.

I am lost on this issue as when i took a measurement on the new battery while running it too was only sitting at 11.8 volts instead of 12 that it needs. Is there an issue with the alternator I have or could it be my belts? I haven't felt or heard any slipping while driving, but those two would be my only good guess.