What's this?

[BadDecisions]

I'm trying to rewire this boat and came across this. What is it.. isolator?? Is it necessary? It doesn't make sense to me.. 1 wire to batt +, one wire to batt switch, one wire to terminal block

[belizesailor]

Maybe an ACR?

What is the terminal block? A positive bus bar?

[BadDecisions]

Yes positive bus

[BlackHeron]

Battery charge isolator.

Something like this:
https://www.amazon.com/dp/B0081SB8YA..._JGK-Eb0DAT6A7

[stormalong]

Yes, it is a charge splitter intended to charge two batteries from one alternator. This is not a good way to charge two sets of batteries. There is a voltage drop across the splitter. A splitter is made of two high current diodes that prevent one battery from pulling power from the other battery.

From your description of how it is wired it might not be doing anything. Does you boat have two battery banks? The way these should be wired is the input goes to the alternator output and the others go to two the battery banks.

The problem with these is the voltage drop across the splitter and where the alternator senses the battery voltage. These undercharge the batteries and shorten their lives.

[BadDecisions]

Thank you for the help. Looks like I'll be getting rid of it. I have a house bank and a starter batt. But it's not wired that way. I think I just need a DC to DC charger for solar and wind. I just wasn't sure what that was and the way it's wired had me really confused. Thank you for the replies

[BlackHeron]

Replace it with one of these. Simple install.

https://www.amazon.com/dp/B000OTIPDQ..._9iM-Eb4CQJXPP