Dual Batteries........Which Type?

LuvBoating

Senior Chief Petty Officer
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Mar 16, 2009
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In late Feb 2012, had a Dual Battery Set-Up installed in our boat. Perko Switch with Barracuda Starting Battery (for "starting" as #1) and NAPA Starting Battery (as "house"-#2). Having trouble w/the Barracuda battery and marine mechanic says that we should get a new one. When I told him that I read an online article stating that a dual battery setup should be a Starting battery and a Deep Cell battery he told me "you don't need that". "You'll do fine with two Starting batteries b/c you aren't running anything big to be using a Deep Cell for". This is true. All we run when tied at dock is a cd player. He told me to get another Starting battery to replace the Barracuda one.
What do you think? Will two Starting batteries work for us?
 
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ihearth2o

Petty Officer 2nd Class
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Aug 18, 2014
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I wouldn't worry about a starter battery. Yes, those things have higher cold cranking power but unless you plan to boat in the winter, you won't really need it. I prefer two deep cells for all the rafting up we do. If you have room, I would go with at least one 27 group. Also, if you do not already have an ACR, I would highly recommend.
 

LuvBoating

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One thing he was VERY adamant about......"don't get a deep cell.......you don't need it." I do have to say, he knows, and has worked on our boat before. We don't "raft up" or anything like that. Like I said, the only thing we do is cruise around and sometimes tie up to local dock and turn on the cd player.......nothing else b/c we don't have anything else. We don't sleep on our boat, so don't have to think/worry about running cabin or deck lights. I have already looked at a NAPA Starting Battery of 1,000 CCA. We already have a NAPA Starting Battery in the boat and it seems to be doing fine. Actually, it appears that the NAPA battery has outlasted the Barracuda one. The NAPA battery came w/the boat and was bought by previous owner in Feb 2009. The Barracuda battery was bought May 2011. The mechanic recommended that we get two new batteries, but financially we can only get one for now.

Just how long does a marine battery last? We are pretty much "fair weather" boaters and don't take our boat out nearly as much as younger folks would. We are in our mid 60's.
 

cdn1972

Seaman
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Aug 4, 2009
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One thing with batteries is any can and will fail. Another thing to look for is a drain in the battery system and that if a battery switch is used it is wired corectly so both batteries get recharged automaticly or cycle the switch manually so both batteries get used and recharged. Some batteries when they reach a really low state of charge require a shop charger to re-start them as most alternators on boats are low amp and if made to recharge deep cycle types can ruin the charging system working them selves to death. Take the battery out and have a shop attempt to recharge it and re-test it.
 

alldodge

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IMO you want a starting battery to start your engine, now you could get a so called dual purpose battery for cranking, so long as you had at least enough amps to fire up your engine (Min 450 for 4 cyl, 600 for 6 cyl and 800 for SB 8 cyl). You want a deep cycle battery for the house battery because it can take draining it better, A starting battery cannot take draining it much below 60% without damaging it.
 

NYBo

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Oct 23, 2008
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IMO you want a starting battery to start your engine, now you could get a so called dual purpose battery for cranking, so long as you had at least enough amps to fire up your engine (Min 450 for 4 cyl, 600 for 6 cyl and 800 for SB 8 cyl). You want a deep cycle battery for the house battery because it can take draining it better, A starting battery cannot take draining it much below 60% without damaging it.

^This. People even use deep cycle batteries to start big blocks with no problems.
 

ihearth2o

Petty Officer 2nd Class
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Aug 18, 2014
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sometimes tie up to local dock and turn on the cd player.......

This would be considered rafting up. Anytime you are just sitting on the water not cruising usually anchored or tied up. Not sure why your mechanic would be adamant about not getting a deep cell. You may not be running anything big but why not have the extended battery life on hand just in case. You would be surprised how much running a cd player would drain even a deep cell battery. I've heard of kids turning on radios without parents noticing and drained the battery while on the water for the day.

I just changed one of my deep cell batteries a 27 group with the same size. Been running 2 deep cells for years. In fact, the deep cell I just replaced lasted me 6 years, it was still powering all my accessories, blower, etc until the day I replaced it. Only reason I replaced it was because it just didn't have the cranking power it used to. The engine would turn over but no fire.
 

Grandad

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Jun 7, 2011
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I've installed 2 Group 27 deep cycle batteries connected by a "1-2-Both" switch. I like simplicity. I run everything including the engine (4 cyl I/O) off one battery at a time, never both. I feel that I'm protected having one "fresh" battery always in reserve. I will often stop at a convenient time and switch from one battery to the other, just to confirm that both are in good fully charged condition. I also have installed a small (3.3 Amp) battery charger/minder/maintainer that I plug in when the boat sits on the trailer which unfortunately is most of the time. The maintainer switches between batteries using only the manual 1-2-Both switch. It's simple and effective. No problem ever cranking the engine. I replace the batteries when they are 5 years old, even if they are still operable. I figure that at a cost of about $20 per year per battery it's a small price to pay for peace of mind, rather than getting the maximum longevity from the battery. - Grandad
 

ihearth2o

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Some batteries when they reach a really low state of charge require a shop charger to re-start them as most alternators on boats are low amp and if made to recharge deep cycle types can ruin the charging system working them selves to death. Take the battery out and have a shop attempt to recharge it and re-test it.


Most boat alternators have charging amps of between 25 - 75 amps unless an upgrade is done. Even at 25 amps though, it will charge a ~100ah deep cell battery (27 group size) in 4-5 hours. That's a long time to be running your motor continuously. I would think that you would shut down your motor way before you overwork an alternator. At 75 amps, that's a couple hours to charge the same battery and that's if the battery is fully discharged. It's certainly conceivable that you would run your engine for 2 hours but that's hardly overworking the alternator IMO.
 

Silvertip

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Sep 22, 2003
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28,758
So what was the reasoning for NOT using a deep cycle battery on the "house" side? Just because he said you don't need one doesn't mean you shouldn't install one. Deep cycles are appropriately named for a reason -- they can be deeply discharged without damage. Not so for starting batteries. Why limit yourself. Should you install additional accessories, the electrical load suddenly makes a deep cycle battery very necessary. Even a dual-purpose battery is better on the house side than a standard starting battery.
 
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