Batteries charge

14.2 to 13.7 is nothing to worry about. Most systems have habits and yours, for a long time, was a habit of staying at 14.2 while charging. Then you changed batteries and alternator, now it's habit seems to be about 13.7. No problem at all.

Resting voltage or state of charge is what you need to watch. What does it sit at when everything is off? Should be around 12.8 with no significant draws on the system (key off, no heavy loads like inverter, etc.)

Anything north of 13.2 while running is fine.

 

Typically you need to feed the batteries with at least 13 volts to maintain a charge. 13.5 to 14.5 volts is a pretty average charging voltage range on most 12 volt systems.

 

check your grounds, all of them.

 

Could be the other set of batteries needed the 14.2 to stay charged and the new set only needs 13.7. If they stay charged with less voltage needed by the alt that is a good thing. Alt works less as hard to keep batts happy. Like @AModelCat said. It sounds healthy to me.

 

you are welcomed.