Adding second battery, need input

clark98ut

Recruit
Joined
Apr 30, 2003
Messages
3
We just bought a 00 Caravelle Interceptor 212 and would like to add an extra battery to the boat. I've searched quite a bit for information on batteries and wiring, but am still a little confused. <br /><br />I have picked up a second battery (largest Deep Cycle that Sears had) already and just need to know how to wire it. I'm thinking all we'll do is add an isolator so that both batteries will charge off of the alternator, but wanted to make sure that is ok. We physically disconnect the batteries after we're done boating each time and if we were in a pinch and the starting batter was dead, we could always move batteries around, so I'm not too concerned with adding a switch. I also think I've seen enough info on how to wire the isolator that I'm not too confused with that. <br /><br />My main question I guess, is how does the second battery need to be ground? Can we just run a wire from the second battery to the first or does it need its own seperate ground? Or, does it need a ground at all? I know we need any accessories to be ground to the battery, but is that it?<br /><br />Any input would be appreciated.<br /><br />Thanks,<br /><br />Dan
 

Cobotr

Seaman
Joined
Mar 26, 2003
Messages
69
Re: Adding second battery, need input

You can either run a ground cable from the negative of the new battery to the negative of the old battery (you still will need to use the existing ground wire from old battery to engine), or run a ground cable from the negative of the new battery to the engine block.<br /><br />Would recommend you rethinking your decision of the battery switch. So many advantages to having the switch. Such minimal cost and labor involved to install one. Also, if you will be disconnecting the batteries as you stated, but will be leaving the boat in the water, you'll be removing power from the bilge pump. With the switch you can disconnect the batteries from the boat wiring (just by turning the switch) yet still have the bilge powered if needed. That is if the bilge has a float switch and it's wired straight off the battery as it SHOULD be. (If it's not already)
 

clark98ut

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Joined
Apr 30, 2003
Messages
3
Re: Adding second battery, need input

Thanks for the quick reply.<br /><br />Actually, we don't keep the boat in the water so that wouldn't really be a concern. It goes home with us after we're done for the day.<br /><br />I'll be sure and check out the switches, but when it comes to electrical, I like to keep it as simple as possible!<br /><br />Thanks,<br /><br />Dan
 

petryshyn

Commander
Joined
Oct 3, 2001
Messages
2,851
Re: Adding second battery, need input

I'd forget the isolator and stick with a battery selector switch....this will allow you to charge and start off of each or both batteries....<br />
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clark98ut

Recruit
Joined
Apr 30, 2003
Messages
3
Re: Adding second battery, need input

I'm having a hard time visualizing how boat electrical/charging systems are setup. I have a fairly good grasp of automotive stuff, but this is all new to me. So, with that said....<br /><br />On our boat, there is one main power wire (+) that runs from the battery to somewhere on the engine. I'm assuming it goes to some sort of distribution block although it looks like it goes to the starter. The battery is ground to the block, but there are also a ton of other wires tied to the negative side of the battery. <br /><br />Does that mean that the alternator charges the battery through the main red wire that I'm seeing connected to the positive side of the battery? Which in turn would mean that according to the diagram above, I'd connect that wire to C?<br /><br />Also, if that is correct, would I be correct in assuming that if the switch is in the "Both" position it will charge both batteries, "1" will charge the starting battery, and "2" would charge the deep cycle? Ditto for pulling power from those batteries?<br /><br />Thanks again for all the help!!!<br /><br />-Dan
 

Boatist

Rear Admiral
Joined
Apr 22, 2002
Messages
4,552
Re: Adding second battery, need input

Dan C.<br />I am not sure if you have a Outboard or I/O but I really like the battery isolator. With outboards some times not a good idea to try and charge a big deep cycle battery if it is run down. If it is a big outboard with a big belt driver alternator then it is ok. Make sure your battery isolator amps is double what your alternator output is and you will have no problem.<br /><br />If you want to install a switch also that is not a problem and can be very nice if have a dead starting battery. I belive some of the older cheap battery switches have killed more alternator than any other device on the boat. <br /><br />If you decide to go just with the switch and no isolator then get a good switch, only about $10 more. You want a switch that does two things to be double safe. It should make second battery before break first battery and have a alternator field disconnect circuit.<br /><br />Reason I like a battery isolator is do not have to mess with switch at all to charge both batteries. You can run all your non boat stuff all day or night and the starting battery will still be good. Start up and head home. With the switch if both batteries charged can start in both and charge both ok but if plan to stay all day or night and run your electronics then must go turn the switch to 1 so do not run down your starting battery. Now if your deep cycle is run down must start in 1 postion then to charge the second go back and turn to both. Now if you go just a short distance and stop but forget to go change the switch back to 1 then the deep cycle drains your starting battery and your dead in the water. If you get the cheap switch with out the alternator field disconect and with the motor running you turn the wrong way and go to off your will very likely need alternator repaired.
 
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