Sounded like a bad cell in the battery. I had one replaced under warranty awhile back on one of my vehicles. I've got a battery tester so it was easy for me to see that the battery was no good. First time I ever used the replacement warranty. Interesting thing about that replacement warranty. Found it only applies to the original purchased car battery. The replacement battery doesn't come with a warranty because it wasn't purchased! Original & replacement batteries were sourced from O'Reilly Auto Parts.