Battery/Isolator question

[CamInc62]

[FONT=&quot]I have a general question as to batteries on my 2011 330 Express Cruiser Yacht. It has a Dual 70 amp input Guest Isolator with 3 outputs. I run two main batteries for the engines, one for the generator and two aux/house batteries. Last year the top terminal of the isolator (main bat term) melted the outer insulation off of the cable and all of the batteries needed water (below plates). My voltage meter did not indicate an issue nor did I need a boost to start.[/FONT]
[FONT=&quot]I did not check the batteries condition when I purchased the boat as everything was supposed to have been in order. I am told that if batteries are over 5 years old then should be replaced and also that all should be replaced as one weak or malfunctioning battery could tax the system and hurt everything else.[/FONT]
[FONT=&quot]I find that hard to believe as that is what I would think is the isolator?s job. I will however check dates on batteries and verify that the isolator wasn?t damaged via a reverse diode test on the unit.[/FONT]
[FONT=&quot]Any advice would be appreciated.[/FONT]

 

[alldodge]

I have a general question as to batteries on my 2011 330 Express Cruiser Yacht. It has a Dual 70 amp input Guest Isolator with 3 outputs. I run two main batteries for the engines, one for the generator and two aux/house batteries. Last year the top terminal of the isolator (main bat term) melted the outer insulation off of the cable and all of the batteries needed water (below plates). My voltage meter did not indicate an issue nor did I need a boost to start.
I did not check the batteries condition when I purchased the boat as everything was supposed to have been in order. I am told that if batteries are over 5 years old then should be replaced and also that all should be replaced as one weak or malfunctioning battery could tax the system and hurt everything else.
I find that hard to believe as that is what I would think is the isolator?s job. I will however check dates on batteries and verify that the isolator wasn?t damaged via a reverse diode test on the unit.
[FONT=&quot]Any advice would be appreciated.[/FONT]

From the melted cable I would see two causes, one or more of the batteries have a cell shorted, and the cable from the alternator to the isolator is not large enough.

If your alternator was replaced with a higher output one and the cable was not changed this could be why the insulation melted. If it was changed out to a one wire type, there could also be issues, and if it goes bad it will boil the batteries.

Disconnect the batteries and let them sit for awhile, then measure the voltages.

The isolator is a set of diodes. The main terminal feeds all the diodes which in turn charges the bats. I would remove the wires off the isolator and set a multi meter on the diode check scale and measure them. Measure from the main lug to each other terminal, on at a time. with the Positive lead on the main, you should read low resistance. Then put the Negative lead on the main and recheck, you should read infinite (very high) resistance