Not fully charging batteries

[Trey7981]

I read on this site to check grounds. I'm assuming the grounds mean batteries, Body, frame, and engine. Well I can only find the battery grounds. Anybody can post a pic of where I need to look I have a 2016 PS isx15. Alt did run at 14.1v but now 13.2v to 13.6v with a meter at the back of the alt. Shop says it's fine. Well something has changed in the 2 years I've owned it. I did change the battery ground and positive cable. And if it matters I have an epu. Batteries where tested. One was bad.