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Old 30-11-2009, 21:14   #1
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Battery Rehab

I just bought a boat with some dead batteries in it and I am wondering what my prospects are of reviving them. They are wet cell and the water in them is just below the tops of the lead (I think that's what it's called). Whenever I turn on the selector switch the meter reads less than 8 volts. I currently have no way of charging them on the boat so I am wondering what to do. Do most auto shops have chargers? If I charge them now in the fall will they hold a charge through the winter? How can I tell if the batteries have been compromised and if I should just junk (recycle) them and get new one's?

I have two batteries in a single bank that are run in parallel.
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Old 01-12-2009, 00:56   #2
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Most auto parts places will test / charge your battery for you. You will need to get it charged or it can freeze in the winter. At 8v it sounds like it will need to be replaced, but you never know until you try.

Once you charge / replace it you could get a cheap solar charger like the one below.




Converts Solar Energy Into DC Current

Super high output will keep all batteries fully charged!
  • Use with auto, marine, truck, RV - any 12 volt battery
  • No installation - simply plugs into the cigarette lighter
  • Compensates for small steady battery drains
  • Mounts to dash or visor
ITEM 44768-3VGA
$19.99


It won't do you any good as far as cruising, but will keep batteries charged while the boat is unattended.
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Old 01-12-2009, 02:36   #3
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Really depends on what sort of battery they are.

If they are deep cycle, it may be worth charging them up and then getting a garage to do a test on them for capacity.


If they are normal lead acid leisure batteries or engine start, dont even waste your time, junk them and replace. They will never be any good even if you get them to hold a charge.
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Old 01-12-2009, 04:20   #4
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Throw em out and start again ....8V is dead....

You have no means of charging them on the boat ?....you need something even if just a solar panel....

There are lots of threads on here about battery types, charging, regulation etc with good information from experienced folk...

Good luck

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Old 01-12-2009, 07:06   #5
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Seems as good a thread to tag on to as any with a question..

Last night I finally got the 2 Intererstate group 24 batteries hooked up to a sears chareger/starter device.

They read at 100% both.

Voltage is 13.0 for one and 13.3 for the other.

So here is my question .....waht does the 13 volts mean to me? I thought the max voltage was 12.6 for a 12v battery......Sorry for the very basic question.

But it seems to me these battries are fine. which mean I have more diagnostics to do to figure out trouble starting
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Old 01-12-2009, 08:42   #6
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The voltage the battery holds after being taken off the charger for a few hours, with no load, is an indicator, but not an absolute determination of the batteries condition.

Take them out of the boat and bring them to a garage or Walmart which has a battery tester. This will tell you with certainty if they are any good. Doing this takes the guess work out of it.

There are also portable battery testers which you can rent or buy.

As previously mentioned, if they are start batteries and not deep cycle batteries, then dispose of them. Start batteries are damaged the first time they completely drain and are left like that for a period of time.
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Old 01-12-2009, 08:51   #7
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To the original question....I've 'revived' batteries in a similar state and had them last for several years afterward. To begin with, you need to add just enough distilled water to completely cover the plates and then some. (You don't want to fill them up completely yet as it will only bubble over from charging, wait until you're done charging to fill them the rest of the way with distilled water.) Once you've added a little distilled water, hook them up to the charger. You should see the meter on the battery charger jump up indicating that the battery is taking a charge, it may not though immediately, so check that you have a good connection on the charging cables, and if you do, sit back and wait. Periodically check the battery with a multimeter to see what is happening (both with and without the charger attached). It may take several days before the battery begins to accept the charge 'normally' again. When the battery has been charged top up the cells with distilled water

As for the most recent question....when batteries are hooked up to a charger, and usually for at least several hours after charging, they give a falsely high reading, usually well above 13v, and most commonly because they are being charged at a voltage well above 12.7v....around 14v or so sometimes. Batteries should be 'rested' following charging for at least several hours (and some claim 24hrs) before attempting to take an accurate reading of the state of charge with a multimeter. A fully charged and rested battery should read somewhere around 12.7v or so at 'full charge'.
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Old 01-12-2009, 09:03   #8
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As previously mentioned, if they are start batteries and not deep cycle batteries, then dispose of them. Start batteries are damaged the first time they completely drain and are left like that for a period of time.
This is a common myth, similar to the false notion that setting modern batteries on concrete damages them (It doesn't, the myth dates back to when batteries were housed in wood containers. Similarly the myth that start batteries are permanently damaged to the point of non-use by one single draining may have it's roots in old battery plate technology). Modern 'start' batteries are surprisingly robust and I've successfully brought them back from the purported 'dead' when all that has happened to them is they've been drained and sat dead for a year or more, and had them last for several years afterward.

Yes, they may need to sit on a charger for several days before they reach the point of beginning to accept a charge again (i.e. 'play possum'), but many times they will be able to be 'revived' if they are in otherwise decent shape.
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Old 01-12-2009, 13:06   #9
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Hmm....I still think any battery that is showing 8V in an open uncharged state is probably dead...
The 100% you see on your charger means nothing...the 13.0V means nothing...many dead batteries "look" OK voltage wise but they have no capacity and when left disconnected quickly drop their voltage due to internal short circuits caused by shed plate material accumulating in the bottom of the cells...sometimes this can be washed out (see Nigel Calders books) ...but its not worth the trouble....just buy new ones....and then look after them properly with a correctly sized charging device and a 3 stage regulator.
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Old 01-12-2009, 17:27   #10
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In a recent development I just discovered that they are two 6 volt batteries that were run in series. I never really understood why someone would have two six volt batteries. How could this be advantageous?

I think I will probably recharge them either way to see if I can get a bit more life out of them. But when I get two new one's I will probably get two 12s. I would need to run them parallel then right?

It's weird because back when I was living aboard Ruffian there was a big bank of 4 batteries and I recall seeing them run in series too, Could this be? Do people ever use a series/parallel setup in a big house bank?
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Old 01-12-2009, 19:07   #11
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Batteries are generally made up of 2 volt cells, they can be in packs of 6 to make 12 volts, or 3 to make 6 volts.

Having 6 volt batteries has the advantage of being easier to manhandle - your batteries are cut in half. Also, a possible advantage is that if a cell drops out you may only have to replace 3 cells instead of 6.

I have 10 x 6 volt batteries, wired series/parallel. Fitting them was a lot easier on the back than 5 x 12 volt batteries would be.

In operation they are exactly the same.
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Old 01-12-2009, 19:16   #12
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Having 6 volt batteries has the advantage of being easier to manhandle - your batteries are cut in half.
These things were not easy at all to man handle. They weigh a million pounds. So in essence all I really had in my boat was one 12 volt battery?
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Old 01-12-2009, 19:31   #13
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These things were not easy at all to man handle. They weigh a million pounds. So in essence all I really had in my boat was one 12 volt battery?
If it was an equivalent capacity (same amp hours) 12 volt battery it would have been like handling them both at once.

Yes, 6 + 6 = 12.

There's different ways to do it - you can have 6 volt batteries in series, you can have smaller 12 volt batteries in parallel, or you could just have one big 12 volt battery. (Within reason)

If the overall volts and amp hours are the same then in operation it's all pretty much the same. Just that having the battery bank divided into smaller "chunks" makes handling them easier. It usually costs a little more though.
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Old 01-12-2009, 20:10   #14
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It ain't dead until you prove it won't hold a charge. I had a sealed Delco Remy bettery that I drained about 3 times over it's life, once in the first year. It soldiered on for 10 years total, & the last time it died (after an alternator failure) it wouln't come back.

Add distilled water to your battery until the plates are completely covered, charge it, & see what the voltage is after 2 or 3 days. If it reads 8 volts after that, then you've proven it's dead. Given the cost of batteries, I think it's worth the effort.

Also, here's some food for thought:
The only way that a battery can freeze is if it is left in a state of partial or complete discharged. As the state of charge in a battery decreases, the electrolyte becomes more like water and the freezing temperature increases. The freezing temperature of the electrolyte in a fully charged battery is -92.0oF. At a 40% state of charge, electrolyte will freeze if the temperature reaches approximately 16.0oF.
(from Trojan Battery Company )
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Old 02-12-2009, 08:16   #15
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These things were not easy at all to man handle. They weigh a million pounds. So in essence all I really had in my boat was one 12 volt battery?
Uh, not exactly. What you probably had/have is the equivalent of a deep cycle 12v battery with massive capacity (220+ah?), or in other words, an 8D battery. Go price an 8D battery (and check out the weight), and then price 2 Trojan T-105's, and you'll see why many people have the T-105's.

I've actually been using an 8D battery recycled from a Caterpillar D8, and it's a real nutbuster to move.
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