Third battery
 

I have two engines, and two battery switches. I just installed two stereo amps in my cabin today. I ran two 6 gauge wires from battery #1 in the bilge to the third battery i installed in the cabin closet. i would like the third battery to get charged from the alternator, but I dont want it to draw from battery #1. Now what?? Isolator?

Isolator

Yup, isolator.

all you need is a 250 watt diode in the wire that ties the third battery into the other two. then the current will only flow in one direction. 5 bucks at radio shack or 10 bucks at any electronics store.

I have a extra Professional Mariner 3 pole battery isolator from my 382 Formula if you are interested.

reddog, how much??

Looks just like the one in the diagram in Offthefront's post #4. Will get back to you on price later tonight.

stevexsm, is that diode u.s.coast guard approved??

I'm thinking a diode will let the battery charge but not disharge into the other batteries ? But it wont keep it from over charging ? Or can a Diode "shut off" at a specific Voltage ? I cant remember ....m