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Old 23-09-2011, 04:21   #1
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New Batteries

I just got three six volt batteries for free, problem is that the boat's systems are all 12 volt agm. If these are lead acid batteries is there any way to include them into the system? Could I use them as a new bank and just wire them in series? What happens with the charger being set for AGM?
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Old 23-09-2011, 04:35   #2
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Re: new batteries

Three 6 V batteries is not a good fit for a 12V system. You know the basic battery rule I assume. Connect in series you add the voltage so 6V + 6V = 12V but the amp hours don't change. Connect in parallel and the amp hours add up but the voltage stays the same.

So you could take 2 batteries in series to add one 12V bank to your boat. You could buy one more identical 6V to pair with the third freeby to make another.

You might be tempted to parallel 2 of the batteries and put that pair in series with the third to make a 12V bank. Don't. It will really foul up the charging.
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Old 23-09-2011, 22:17   #3
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Re: New Batteries

Mixing battery types i.e. lead acid/AGM is not recommended at all. AGM batteries take higher voltages to charge them. It might only be a volt or two but it would end up frying your lead acids eventually. Only in a great need should you mix batteries.
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Old 24-09-2011, 06:04   #4
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Re: New Batteries

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Originally Posted by IceMan View Post
Mixing battery types i.e. lead acid/AGM is not recommended at all. AGM batteries take higher voltages to charge them. It might only be a volt or two but it would end up frying your lead acids eventually. Only in a great need should you mix batteries.
BUT THERE FREE
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Old 24-09-2011, 06:24   #5
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Re: New Batteries

Skipmac sums it up quite well. But in any case if you want to use the batteries they need to be in a separate battery bank from your original AGM battery bank.
- - Charging the liquid lead acid 6V arranged in series to get 12V will not be a problem with your charger set on AGM setting. They will just not get totally up to full charge. But they will function for whatever their remaining life is.
- - However, the charger does need to be one with multiple charging feeds. That is, you should not use the same wire off the battery charger to feed both the AGMs and the old free batteries. What you need to watch for is that if you were to parallel the AGMs and the free batteries there is the possibility that the free batteries will develop an internal short and drain the AGMs and kill them. For the same reason don't run the two batteries banks in the "Both" position of a battery switch.
- - The main problem with "free batteries" is where the heck you are going to put them. You need to build a new battery "box" where they can be securely tied down to keep them from "spilling" and they need to be vented so fumes don't get at other items in the boat.
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Old 24-09-2011, 06:26   #6
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Re: New Batteries

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Originally Posted by JusDreaming View Post
BUT THERE FREE

Anything free is worth exactly what you paid for it.
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Old 24-09-2011, 16:59   #7
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Re: New Batteries

damn and I was really excited about a wind fall of batteries but it sounds like more trouble than it's worth
BUT THERE FREE
It sounds like I would also need a new battery switch, three position, as everything on board is wired and laid out for a two bank system. Or they would end up at some point being combined with the existing,(NEW), batteries. They are only two months old.
Oh Well "If it seems to good to be true, it probably isn't"
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Old 24-09-2011, 17:21   #8
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Re: New Batteries

Quote:
Originally Posted by IceMan View Post
Mixing battery types i.e. lead acid/AGM is not recommended at all. AGM batteries take higher voltages to charge them. It might only be a volt or two but it would end up frying your lead acids eventually. Only in a great need should you mix batteries.

According to http://www.windsun.com/Batteries/Battery_FAQ.htm#AGM, or Absorbed Glass Mat Batteries the charging voltage is the same for AGM and flooded batteries but the rate of charge is higher.
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Old 24-09-2011, 21:07   #9
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Re: New Batteries

[QUOTE=JusDreaming;782554]damn and I was really excited about a wind fall of batteries but it sounds like more trouble than it's worth . . ./QUOTE]

It is just a matter of what you use them for.
- - If you have an electric windlass on the bow, they would work well up there.
- - If you have bow thrusters or stern thrusters, they might be good there.
- - Drain the acid out and they make good mooring anchors.
- - If your boat naturally "lists" a little they can be used to even up the boat.
- - They can be charged via a battery combiner system that first fills up the ship's batteries and then when they are full, charges up the new free batteries. A simple on/off battery switch can bring them on-line when needed.
- - You can sell them to somebody who has 6V batteries.
- - And probable a list of a hundred other possibilities.
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