charging issue question

So I have been having this 'issue' since I bought the boat. I have 2 batteries (one bought new when we bought the boat and the other bought new 2 years ago). I have a 4 position Perko switch and an isolator. When the switch is on the engine battery my voltmeter reads about 11.5 volts (confirmed with voltmeter). If I turn my blower on it drops to 10.5. I have never had any issues out on the water but we are on the Ohio and only run maybe 1 hour at a time max. When we anchor I switch to the house battery. Yesterday I forgot to switch back to the engine battery and noticed my volts were about 12.5 when running on the house battery?

I looked at this problem a couple of years ago and had the alternator tested and rebuilt and also tried a brand new alternator with the same results. I gave up on the issue as it had never caused any problems but after yesterday I'm wondering if this may help to narrow down my problem? Sound like a bad ground or wire? I had checked and cleaned a few grounds before and reinstalled with dielectric grease but haven't gone through all of them. Based on what I saw yesterday it would seem to me that it might be bad wires or connections since one battery gets more charge than the other? I'm familiar with DC electrical systems but far from an expert.

Any suggestions on where to start looking or if my theory is accurate?

Are they both the same type of battery?

So one battery is 2 years old and the other is how old?

Is your engine battery the oldest and showing a lower number?

The house battery is 3 years old from Auto Zone (Marine-Deep Cycle). The engine battery is 2 years old from West Marine. The engine battery has the lower input. Had the same issue with the original engine battery that was in it when I bought it. But even with just the engine battery connected it is still low. I was thinking along the lines of if the alternator is putting out 13.7 volts but battery 1 gets 11.5 and battery 2 gets 12.5 (still too low) then since there is a difference then it would likely be something that is independent of the 2 batteries? Thinking the cables? Maybe they are both 'bad' but the engine battery cables are worse than the house battery?

Also, I have a Standard Horizon GX1700. When I hit my trim tab buttons a 'Lo Battery' message pops up on the VHF. But I knew this because I already confirmed low voltage at the dash with a voltmeter. But in 3+ years I have never had any issues, probably because my trips are short though?

Trace the low voltage back towards the alternator. See where you're losing it

scoflaw said:

Trace the low voltage back towards the alternator. See where you're losing it

Click to expand...

Good idea. Have to give that a shot. Thanks!