Weak battery or aging starter motor?
 

2013 Anniversary Edition Corvette. Very low miles. Usually garaged and on tender. Initial start up is good. While driving the battery meter reads 13.5. If I make a stop and turn the car off upon restart the starter turns over slower and longer before the car starts up. Battery is 2 years old and starter is original equipment. In as much as the initial start up is good I am thinking the starter is likely OK . Time for a new battery?

Get it (battery) load tested.

^ Load test battery, may very well be defective/failing.
Not driving long enough to fully charge, IIRC >20 mins, has been behind 'bad' batteries also.
Charge is at 13.5. Battery? :confused2:
My '08's always slightly >14V @ start-up & operating. Always on maintainer.

Just because a batt is fairly new doesn't mean it can't be defective. Over my years i've ran across several batts that just didn't last like they should have. If you purchased it take it back to them and have them test it. If bad maybe theres some warranty on it. If no chance there then i'd bite the bullet and buy a new one and at least take the choice of a new batt out of the equation when trying to chase down the problem......good luck

Had similar symptoms and it turned out to be a bad starter solenoid. The plastic around the BAT terminal had cracked to the point the terminal could move, caused long cranks and voltage drains, but only when it landed in just the right place. I think it overheated from charging the battery connected to the BAT terminal in the fuse box instead of direct to the battery. I just replaced the starter since I'm at 95K and didn't want to wait to get the solenoid from an online supplier. Easy to diagnose from below.

I'd say bad starter, or connection at the starter. If a good starter is cranking slowly, the voltage will be very low during cranking. But on our cars, when the voltage drops, the computer browns out and will stop commanding the starter to turn. That's why C6s with weak batteries don't crank slower and slower - they just suddenly won't crank at all.

Many thanks to all for your comments. Starter and alternator are 6 years old. I will have the Corvette tech who services the car evaluate the starter and alternator and change out either or both if questionable.

Since your not servicing the car yourself, really a mute point, but!!!
https://www.corvetteforum.com/forums...nator-fix.html

Next is to clean and check the connections on the charging system, including the connecting point of where the alternator cable to battery cable connect on the starter solenoid. Hence loose connection there on the starter solenoid will cause both starting and even charging problems.

Then, do a quick amp draw test of the battery to make sure it's still good, or if the problem is that the battery is just low on water instead.
https://www.corvetteforum.com/forums...intenance.html