14.8 volts normal ?

Could have a battery with a bad cell, and the alternator could be over charging to get it back up, Im having the same problem, my alternator is working fine but my volt gauge is reading about 14.5 go 15 and it's fluxuating.

 

Actually, flooded cell 12V batteries are fully charged to 14.4 volts at 25°C.

Separate each battery and fully charge and let rest half a day then check standing voltage. 12.8V is good. Mine are showing 12.88V each and they are over a year old and fully charged last week. I frequently (sometimes by accident) give them an equalizing charge. That is slightly overcharging for an hour or so (maybe 15V) to bring any weak cell up and the over charge will theoretically boil down the stronger cells, thus "equalizing" them.

A weaker cell never brought to full voltage will get weaker and weaker to the point it reverses (around 10V or less IIRC) and shorts out the battery. Then it sucks the juice out of all the others in the bank.

Lots of battery info on the net these days with everyone going solar and living "off grid".

 

My truck is on 12v less

 

What should change alternator or battery first

 

Change nothing. Troubleshoot first, its cheaper. No sense throwing money away unless you know what the failed component is.