When fully charged my batteries sit at 18.3V, car off when used for two days no charging it reads between 16.8 and 17.2V. If you are running an external regulator you need to turn it up it should be in the 17's for a standard cell, AGM should be charging around 19-19.2V .. Polo..
PS- Float voltage is gonna be a lot higher and necessary to fully charge those batteries.
Polo..