Third Battery?

[MCNPathfinder]

Hey everyone, quick question before I make a huge mistake. I have an extra battery laying around that I'd like to put in my boat to run the audio off of. Right now I have a 4 position Perko switch (off, 1, all, 2). What I'd like to do is run a second battery off my secondary battery in parallel that goes to my amps. I would run it in parallel so I have 12 volts, but the idea is to get the alternator to charge all 3 batteries while running. First question, do you think this will work? 2nd question, how do I do this safely? Mainly I'm wondering if I have to fuse the line running from the second battery to the third battery. The batteries will be about 4-5 feet from each other so I was going to use a run of 4 gauge. Lastly, is this going to be too much for my alternator to handle, charging all 3 batteries? Pretty sure it's the stock GM alternator they use on the 305 (unless you're supposed to use a marine certified one, then it's probably that, I don't know a whole lot about the engine).
Thanks!
Not that it matters a whole lot, but once everything is installed, I'll be running a 2,000 watt RMS amp to 2 12" subs, and a 4 channel amp running at 4 x 120 watts RMS, plus the lame 20 watts RMS to 2 speakers that my deck puts out.

 

[mark1905]

Re: Third Battery?

Yes, it will work fine. I run my 2 batteries in direct parallel with no fuses or switching with zero problems.

YES you need to be running a marine alternator! ..and yes, with 3 batteries.. it would be advisable to upgrade that alternator to at least a 105A model. They're under $70 from DB Electrical. Make sure you upgrade your alternator charging and ground wire to 6AWG marine cable and make sure to use nothing but marine power cable for all of your stereo installation.

 

[Scott Danforth]

Re: Third Battery?

I have two house batteries on position 2. no problems.

 

[MCNPathfinder]

Re: Third Battery?

Sweet thanks for the help. I figure it's a marine alternator. From what I understand if you use a car alternator it can spark and ignite the gas fumes right? I think I'm over that 105 amp on my existing one, so I should be good to go. Thanks again for the help!