I had an Autocraft Silver series 625 CCA battery in my car that served me well for years, until it got old and tired and I replaced it with the exact same model. The car started like a champ when cold, but after I stopped for anything like fuel or any other short stop it would crank very slow and it damn near couldn't start the car, leaving me sweating. I took the battery back to Autozone and they even heated it up and tested it but it was fine. They tested the ignition system. The next thing I was worried about was heat-soak on the starter, but the test said the starter and alternator was fine, BUT the test cancelled itself due to voltage loss. And with the ignition off it was reading a 3 amp drain that the guy said was pretty significant. So what should I focus on at this point? Of course it started pretty well during the test, slow to start then picked up and kicked over well and I did cruise it around for 20 minutes to get to full temp.
The only other thing to change besides the batter was I had the heads rebuilt. There was some serious exhaust valve leakage and it has more noticeable bottom end. Even if that is making more resistance, the original manufacturer recommended battery amps was 325.