I have an older battery in my C-class (over 5 years), so I decided to have it tested at the close by Advance Auto.
They used the machine which prints out results, and the battery was showing 12.25V with 543CCA (battery is AGM with 800CCA). All this at temperature of 47F.
The car starts with no issues, and I have a jumper box in my car. But should I still go ahead and replace the battery, as it does say GOOD on the piece of paper, but the sales person at Advance is still telling me I should replace the battery.
Kinda of an either or deal. The battery is good. You have proof of that printed on a piece of paper.
For me, NO, I would not replace the battery until I needed too. I mean that is why I have a back up jump pack to begin with. Once it gives me trouble, then I remove it and replace it. No reason to remove it until I am having and issue. But that is just me. I am a mechanic after all.
Now when I test a battery, I use a Battery Load Tester not just a volt meter. And if under load it is holding to 12.25 volts, there is no way i would replace the battery. Anything over 10 V under load is acceptable 800CCA.
Finally, looking at it from the Salesmen stand point. If he tells you to replace it and you do he has a win win situation. One, he made a sale which is his job after all(he is not a shop mechanic, he is in sales). Two, he is all but guaranteed that you will not have a battery issue next week if he sells you one.