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post #1 of 30 Old 11-26-2006 Thread Starter
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Battery charging

I have two 12v batteries hooked up in the usual serial way to meet minimal requirements. Can I hook up a smart charger to one of them, turn the battery switch to both, and charge them both? Or do I have to charge them separately?
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post #2 of 30 Old 11-26-2006
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Your question isn't real clear but Im thinking the answer is you need to charge them one at a time. Put the smart charger ahead of the switch then switch it back and forth or get two chargers.
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post #3 of 30 Old 11-26-2006
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drynoc, two 12 volt batteries in series is for a 24 volt system. I assume that you mean they are connected in parallel. You certainly can set the battery switch to both and charge both at the same time. That is exactly what a battery combiner does.

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post #4 of 30 Old 11-27-2006
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The batteries must be exactly alike in every aspect to do that. Most are not.
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post #5 of 30 Old 11-27-2006 Thread Starter
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Battery Charging

They are identical batteries bought from West Marine three years ago. And right, I meant to say that they are in parallel. But I tried to charge them both at the same time with the switch set to both, and it didn't work. The charger said "full" after a while, but I was able to hook it up to the other battery and it charged that one separately.
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post #6 of 30 Old 11-27-2006
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Wildcard said:
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The batteries must be exactly alike in every aspect to do that. Most are not.
Wildcard, I believe that to be another of boatings "Old Boater's Tales". Read the following thread carefully if you wish. I think it refutes the belief that parallel batteries need to be "identical in every way" quite well. Don't you?

Paralleling Batteries

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But I tried to charge them both at the same time with the switch set to both, and it didn't work.
drynoc, perhaps you could explain your wiring setup and problem in a little more detail. If your batteries are wired to the "Bat. 1" and "Bat.2" terminals on your selector switch, and the switch is in good working order, then setting the switch to both should effectively parallel the batteries.
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post #7 of 30 Old 11-27-2006
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Battery charging

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Originally Posted by drynoc
They are identical batteries bought from West Marine three years ago. And right, I meant to say that they are in parallel. But I tried to charge them both at the same time with the switch set to both, and it didn't work. The charger said "full" after a while, but I was able to hook it up to the other battery and it charged that one separately.
The easiest way to make sure you are hooked up correctly is to measure the voltage on both batteries as you are charging and switched to "both". You should measure 13.3 to 14.5 volts, depending on the battery charger and battery type. If you measure less then 13 volts you have something hooked up wrong. If you are using a "smart" charger that calculates amp-hours out vs. amp-hours in you will get an incorrect "full" indication.

Lead acid batteries take 12 to 18 hours to charge to their full capacity after they reach their float voltage level. As long as your charger is maintaining the voltage at the correct level you will charge your batteries. If the voltage drops after the charger indicates full, you have a problem. There are so many different types of chargers out their it is difficult to know what it does without a full specification or operating characteristic.

There are two types of fools...

One says this is old, and therefore good..

The other says this is new, and therefore better...
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post #8 of 30 Old 11-27-2006
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Dave, I have a similar question, have read your various posts, but my understanding is more limited, so I'm not sure I'm following your advice properly.

I have two group 27 gel cell house batteries in parallel, and one group 24 wet cell maintenance free starting battery, all hooked up to a red charging switch that reads 1,2 or both. I also have shore power and a Link 10 inverter/charger.

My question is: am I causing damage to any of the batteries by charging them with the red switch on "both"--should I be charging the house batteries and the starting battery separately?

Thanks,
Frank.
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post #9 of 30 Old 11-27-2006
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Dave,

I was typing a reply to this then saw yours.

I wonder if he is using a portable charger? That is my guess. Maybe it is seeing the batts full after bulk and shuting down to read a false full? Can't he "fully charge" them, dissconnect them from the system, and check his open circut volatge for a SOC? Depending on the batteries, he should show 12.8 or greater, if I am not mistaken, at 100% SOC. He could also sepearte the batts and check the SOC independently. Assuming they are both not full, it is likely he has a charger problem and it is not accurately reading the batteries.

Thoughts Dave?

I think this underlines the importance of a good, multi-stage, deep cycle battery charger. As expensive as batteries are, it will make you money.
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post #10 of 30 Old 11-27-2006
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Frank,

Dave is much more of an expert than I am (FOR SURE), but gells charge different than wets. They cannot be in the same charge system. You can quickly cook a gell if it is over charged. You will need to change the wet to a similar gell or vice-versa, or get a seperate charger that you can set the wet or gell on. Make sure the charger on the gells is set to gell per the mfg reccomendations.
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