I have a Duracell agm battery in my car. Without looking it up I'd say it's 4 or 5 years old. The car seems to start ok, but I don't want to wait until I break down. The battery is showing 12.6 volts in tuner studio, with the car not running. Is it time to go battery shopping, or is that voltage acceptable?

 

12.6 volts is good, and the most voltage you’ll usually see out of any battery with the car not running. That being said, doing a load test with a proper battery tester will tell you more than just the key on engine off voltage will.

I think autozone or the like have battery testers you can borrow or use in the parking lot.

 

My cranking RPM is slowing down with my 6 YO battery. I ordered an Interstate today for peace
of Mind. Their P/N is MT-MX-5. 😃

 

I buy my batteries through Costco. They sell Interstate. Great battery for a good price.

 

I also agree that a good battery load tester should be used to test the battery.