Dodge ram 2500 has a low battery voltage even with a new battery

Tighten and clean all battery connections. Test output voltage of your alternator. It should be putting out 14.5 or so volts. If it's not then it's probably going to need to be replaced.

Also what year model is your truck? If older than about 2002 or so might want to tighten and clean the negative battery cable on the frame and motor. If they loose or dirty they can cause the same issue.

Beyond cleaning the battery cable connections, and replacing the battery cables, your alternator might be going bad.

I just changed the battery and alternator on my 2005 ram 1500 and it has a code of low power voltage and ac started to blow hot air and has check gages light on

I dunno why but mines brand new and shows low voltage every dodge I know shows low voltage

I get 14v consistently before and after new batteries. Only 43400 miles on truck hoping this is normal