Batteries not charging help!!!!

[Duramax52513]

I started my truck the other day and my battery light came on and on my dash it said batteries not charging, once I get to highway speeds the battery light goes away and so does the message on my dash, I got the alternator tested and they said its fine, I replaced the serpentine belt because that's what the auto store said, I got both batteries tested and they are still good.

Someone told me I could have loose wiring or a bad connection to my battery guage on the dash or the bearings in my alternator are bad and it won't work at slow speeds. When they tested the batteries they said the voltage regulator failed the test, I just don't know how the alternator tested fine if the voltage regulator is bad?

Anyone else had this problems, I don't have the money to just start replacing stuff untill I fix the problem, please help me out

 

[MACKIN]

I would get my hands on a volt meter start your truck and see what the alternator is pushing back into the batteries. Somewhere around 13.5 ish to 14.5 ish is a decent range.

 

[THEFERMANATOR]

If you used one of the parts store testers, they will often show a bad alternator as good. Those testers have no way to load the alternator to check output, and just look to see if it produces power, and does a quick diode check. Check the alternator with it on the truck. Make sure it is holding at least 13.5, but 13.8-14 is much better and closer to what most hold. Turn on the lights and other loads and see if the alternator can keep up. Or find an actual alternator shop that can load test your alternator and make sure it is holding voltage while being loaded down.