Batteries Dying When Truck Sits Over Night

[brandmid]

Replaced my starter relay, forgot to hook up a wire and the batteries didn't charge and the battery light was on, I found the wire and hooked it up and now when running its a 13.1 volts when its off batteries (which are new) are at 12.6 volts, I did notice that my battery gauge used to be pegged out, as to where it would make my battery light flash and when i would turn on my lights or something volts would go down a little, now even with my batteries charged at 12.6 the gauge shows a little under 1/2 I may have messed up wiring or something I will post pics to help ASAP

sorry for the run along, any help appreciated