GOOD ADVICE!!!!
I recently chased my tail for about 5 hours as my V checks kept showing 12V but every time I tried to start it NADA, yet it had started perfectly 10 minutes earlier.
I did not even consider the battery as I have NEVER had one fail like this in over 50 years, so i proceeded to chase my tail. It was only by chance that I had the meter hooked up and watched it drop to 2v with a load and quickly recover to 12. It was showing V with no load, but had no Amperage/ Current

I have since read this is becoming a not so uncommon occurrence as the battery MFR's are cutting costs by using thinner plates and connections inside the batteries
I will say it was on a tractor with a bunch of safety interlocks so I ASSumed that one of them were at fault again. I can tell you I will not get stung on that one again