Originally Posted by Dog8It
All three batteries will show a charge of 13.2-13.4V upon completing the charge and then slowly settle to around 12.8V.
However, when I come back to the boat a week later, I usually find both of my house batteries down to 12.5V and the engine battery around 12.6V.
These are wet cell batteries correct (asking even though you said they were)
Are you are going only by the voltages? I don't think your batteries are fully charged at all based on what you say. I bet they are only around 80% charged.
Have you measured the specific gravity of the batteries?
You need to measure the sg and charge till they are truly fully charged and only accepting around 2% of amp-hour rating as amps into the batteries at a voltage of 14.2-14.6V. Then you need to check the sg to see if they really are charged.
After you get there you should discharge them to 50% and then do it again and if your charger has an equalize function you should run it after they are charged.
BTW - it doesn't sound your yard guys know much if they have not told you this.