Starter? Alternator? or Battery?

[Tinker]

Hi all,

Had what I thought was a bad starter in my wife`s 190e. Was cranking slow and slower for a few weeks and finally bit the dust in a Target parking lot. Battery appeared strong.

Got a replacement McParts starter and installed it. First cranks sounded great... subsequent cranks sound terrible and ultimately result in the starter not making full contact with the ring gear. Ouch!.

Put a charge on the battery and the car starts strong first few cranks and then again starts to fade.

Battery is about 2 years old. It is a GOOD Interstate monster that put out close to 13.6v sitting (wow) even after it abusing it with the starter. Checking the charge from the alternator and I am reading about 13.8v at idle and with most accessories running.

Is it possbile for the alternator to put out enough voltage but not enough amperage to keep the battery properly charged?

Course of action?

Curious.

Tinker