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Thread: Another Battery Question

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    Member patrickL's Avatar
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    Default Another Battery Question

    Okay, so I'll admit up front that I made a stupid mistake by forgetting to do something I new better than.

    So, I left my Lowrance sounder hooked up during the early fall and it drained my house battery on my boat. It takes a little draw all the time, even when turned off, and I forgot to disconnect it. When I pulled the batteries back just before the first snow I went to top them up and found it was dead. The starting battery is fine but the other is ruined. I tried to charge it but it was drained too far down. Then the charger I have, supposed to be a good one, boiled it when it wouldn't take a charge. Supposedly this isn't odd as it was really drained. The batteries I have are both Optima Blue Tops 34M. Way to expensive for my tastes.

    So for my question. I know you are supposed to match batteries so they aren't draining one another. But a new 34M is $225. I can get a D34M at Costco for $160. They differ just a little but I don't want to match it up if its a problem. The specs can be seen here....http://www.optimabatteries.com/optim...etop/specs.php I know there can be some problems with matching batts with different specs, but then it sounds an awful lot like a tire salesman telling you to get a matched set. So my questions is, does the Perko switch isolate the batteries from one another? I realize in the "Both" position it doesn't, but what about the others? Is it that big of a deal to buy these two batteries that are just a bit different? What are the costs to matching these two batts up? Any other suggestions?

    Also, is there a way to isolate the sounder so it won't draw power? I don't want to have to keep unplugging it or I may forget again.

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    With out knowing how your boat is wired, it hard to give you a good answer.

    If you are charging both batteries at the same time and not using isolation they do need to be the same. That also means you can not charge a new and the old batteries at the same time. If your charge one battery and switch to the other battery you will have no problem.

    You should install a switch to disconnect everything from the house battery.

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    In general matching batteries means you should match them to the same type: Flooded, AGM, or Gel.
    If I remember right the Optimas are spiral wound AGM (absorbed glass mat) batteries.

    Within each type the charging characteristics are the same, which means you can have a small optima and a larger sized optima, as long both are spiral wound AGM batteries of the same nominal voltage.

    If you had a flooded lead-acid battery I would recommend you try a pulsed desulphator, but AGMs are very sensitive to charging conditions and I can't remember what a desulphator would do to them.

    I've used my desulphator to bring back batteries from the dead to 80% capacity that were so far gone most people wouldn't believe they could ever be used again.

    BTW you could always install whats called a "low voltage disconnect" for when a battery gets below a set voltage (usually ~11 volts) it'll automatically disconnect the battery from its load. I think the new blue sea automatic charging relays have one built-in.
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    Member broncoformudv's Avatar
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    Quote Originally Posted by Rutting Moose View Post
    With out knowing how your boat is wired, it hard to give you a good answer.

    If you are charging both batteries at the same time and not using isolation they do need to be the same. That also means you can not charge a new and the old batteries at the same time. If your charge one battery and switch to the other battery you will have no problem.

    You should install a switch to disconnect everything from the house battery.
    Like Rutting Moose said you need a battery switch that will isolate each battery or allow you to run off both or charge both at the same time or you can just turn your batteries off when your boat is not in use then there are no issues with small electrical drains.. Believe they are called Perko switches. Then again this still involves you to remember to do it. Yeah I forgot once!

    Without an isolator all battery experts recommend replacing both batteries at the same time with identical batteries or one will discharge to the other. I have never experimented with this idea and have always just replaced both batteries when one went bad.

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    Member chico99645's Avatar
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    Ditto on the Battery Switch. Also, call or go see Battery Speciallist in front of the Aces Store. Battery Specialist of Alaska. 801 E 15th Avenue, Anchorage, AK 99501 (907) 276-5531 ... The older guy that owns the store (can't remember his name) will give you the strait poop if you can't or can't mismatch the batteries. He gets all my bussiness and I believe still has the Military Contract for Ft. Rich and Elmondorf for Optimas. He is a very strait shooter IMO

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    Moderator Paul H's Avatar
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    No matter what route you go with replacing your battery, I'd highly recomend adding this http://bluesea.com/products/7650



    to isolate your batteries and provide a switch. not shown are in line fuses in the circuit.

    I use an optima for my starting battery and a costco marine battery for the house battery. So far no problems in three seasons.

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    Member patrickL's Avatar
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    Thanks for all the replies and info. So I guess I got a little long winded in my first post. I already have a Perko switch on my boat which isolates the house and starting batts and allows me to run them in parallel for emergencies.

    The problem is, I don't think the accessories are wired correctly in that I can't actually shut them off the battery when I put the boat away for a week or two during the summer. My sounder draws power even when off and this is what drained the house battery. I had the Perko in the "Off" position but since the sounder is directly wired to the house, it can still draw current.

    The first question, is there a way to wire accessories to the house battery that can be shut off so as not to drain the battery?

    Second question, when replacing the one bad battery, do you think I could save a little money and buy one battery closely related to the one I have, such as the D34M, or should I buy the exact model, or should I replace both?

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    Moderator Paul H's Avatar
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    So long as the accessories are wired in after the perko switch, they won't consume power when the switch is turned off.

    My recomendation is to wire a fused terminal block into your system (after the perko switch) and wire your accessories to that terminal block. That way the accessories are isoloated, and protected via the fuses.

    The two systems most likely to fail on a boat are the electrical and fuel systems. Which is why I put alot more $ and effort into the systems I have on my boat than I could have gotten away with.

    Just think, a typical trip out in the boat costs as much as the most expensive battery, so balance out the cost of a spoiled trip to that of a new battery. For me the piece of mind of good batteries is well worth replacing them whenever I'm in doubt.

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    Quote Originally Posted by patrickL View Post
    The first question, is there a way to wire accessories to the house battery that can be shut off so as not to drain the battery?

    Yes, you need to add a 2nd battery sw.

    Second question, when replacing the one bad battery, do you think I could save a little money and buy one battery closely related to the one I have, such as the D34M, or should I buy the exact model, or should I replace both?
    If you are going to charge one battery at a time there will be no problem. If you try to charge them together, yes you will have a problem.

    Pat if you want to talk about it give me a phone call.

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    Member patrickL's Avatar
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    Paul, thanks for the input. Your point about the cost of a trip is a good one. It easily costs a few hundred bucks to head out for the weekend. So the cost of a good battery is really less that the cost of a trip.

    Moose, thanks again. That's what I was thinking. When I'm out running for several days I rely on the motor to keep things charged up. I may run down the house battery running accessories and utilize the motor to charge it back up. Seems like it wouldn't be a good idea to get a batt with different specs if this is what I'm going to do.

    What do you think about putting a 2 or 3 year old battery in the same system as a brand new one? These Optimas can last a long time so I would hate to get rid of a perfectly good battery.

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    Moderator Paul H's Avatar
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    Irregardless of what way you go with batteries, I'd put in the blue sea battery isolater, it allows the engine to charge both batteries as needed, but they are isolated so they won't discharge one another.

    If it was my boat I'd keep the 34m starting battery and use the D34m as the house battery replacement, provided you add the isolater between them.

  12. #12

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    Also, is there a way to isolate the sounder so it won't draw power? I don't want to have to keep unplugging it or I may forget again.

    Instructions could vary from unit to unit but my lowrance gps/sounder directions state that in addition to being fused, the unit should also be switched for that very reason. Easy to install a small toggle switch next to the unit or where ever space permits. Also, I bought my Blue Sea dual circuit acr..part# 7650 form Amazon.com and got free shipping for under $100. Works with alternators up to 120 amps. Don't know if they still carry them but worth checking.

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    If you wire lowrance gps/sounder power wire to the ignition switch acc. side and the memory wire to the fuse panel that go to the main battery switch. You will not need to add a 2nd switch to disconnect the unit. As long as you can remember to turn off the main battery switch.

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