battery or starter issue?

[John]

I took my car out for a spin over the weekend and experienced something that I thought I'd see if anyone might have had a similar past experience with or feedback. I drove the car about 20 minutes and was at operating temp, then stopped to get gas and shut if off. When I went to restart it, it acted as though the battery barely had the juice to turn over the motor. Luckily it caught so I didn't have to crank it more than a few seconds. This has never occurred before. And when I started it up that morning, it cranked with plenty of power.

I did not have the time to look into it once I returned it to the garage and might try to re-create the situation this weekend. The battery I think I can rule out since it cranked over fine earlier in the day-however, I did not try cranking again after I returned home since I was in a rush to be somewhere. And as I said, the car has never done this before and this just came out of the blue. Any thoughts?