[Tkenopic]

Hi everyone
I have 2 batteries that were purchased in 2016. One smelled bad so I popped caps and the water was very low. I topped that up. When I tested voltage the bad battery was 13.5 and it is the house. The starter was 13.0 . Our new radio is displaying an error message saying “high battery”. I’m wondering if my alternator is overcharging? Wondering how I test for that? And what to do about it? Can you adjust an alternator easily? No knowledge in this area. Hi hanks!