Please help really frustrated

[Beach-TJ]

I'm having charging issues with my boat here is my setup I have three batteries one to start and run boat electronics and two to run the stereo equipment all three batteries are marine deep cycles. I recently had all three batteries checked and they are ok. The battery to start the boat is working good no problems but the other two die about three hours of use. My alternator wire runs to the front battery which is the starting battery I then have a battery isolator then its linked to the back battery's all grounds are grounded at the motor. I recently had my high output alternator rebuilt and the volt meter is reading 14 volts why aren't the other battery's charging any help would be greatly appreciated.

I had a similar set up in my last boat, a starting battery and two deep cycles for a house bank, with a battery isolator. The isolator I had required that the isolator be installed between the alternator and batteries. The alternator wire ran directly to the isolator, then a wire ran from the isolator to the starting, another wire ran from the isolator to the house bank (stereo batteries). With this set up each branch coming off of the isolator saw up to 14.4 volts, but the alternator actually put out up to 15.4 volts. The isolator had a one volt drop across it. If your isolator is designed to be hooked up the same way that could explain why your house bank is not properly charging, the one volt drop would only allow the house bank to see a max of 12.4 volts. Note that any alternator is capable of putting out 15.4 volts, it's just a mater of where it senses the voltage. I wound up calling the isolator manufacturer and figured out that I didn't need to do anything extra to get my alternator to function properly with the isolator.

[Beach-TJ]

Did a little searching and I see that your isolator works different than the one I had, so I guess you can ignore my previous post.