Both batteries are over 12v at rest. 13 plus when running.
Cold starts are fine. Engine cranks no worries first try of the day.
The other day, as I drove it more, the starter slowed down more each stop. It got to the point where it would barely crank, I actually had to get a jump.
So when I got home I let it sit for an hour. Cranked easy. If the batteries were dying I wouldn't expect them to get better just sitting an hour.
Just now (cold) I started it and let it run out of gas in the carb. Then cranked it for 10 seconds and it barely slowed down, good healthy cranking. Battery still shows over 12V after the 10 seconds of cranking.
So I am thinking the starter is having problems once it is heat soaked.