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Old 03-28-2015, 12:57 PM   #1
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Angry Batteries Discharged

I've had my boat on the hard since Oct. Like most marinas, this one won't allow a trickle charger or any other electrical hookup on an unattended boat in their lot. I figured with the low discharge rate of 8A8D AGMs, I'd be OK, even with the tough winter here. Well the port bank reads 10 volts and and the starboard is 3. Every breaker is off, as I left it. I checked on the boat regularly and nothing has been running over the winter. Bilge pumps have been idle--the boat is shrink wrapped and no rain has gotten in.

I know far less than I should about this boat's electrical systems (been focused on learning everything but electrical, I'm afraid). I have a receipt back home I can dig out to find their age, but I think the AGMs are about 5 years old. It looks like there's a two-battery bank for each main engine that also provides 12 volts to the house. There's a single 8A8D for the Westerbeke genny.

So my questions are:
  • How likely is it that these batteries are toast? Should I even try to recharge them?
  • If it's worth trying, how would I go about trying to charge them? The Xantrex 40 charger is hard-wired into the boat and it's a 50-amp service. I don't have an adapter or shore source within distance to handle that. (I can string about 150 ft of 110 to the boat as long as I stay with it.)
  • Should I put a charger directly on the batteries and just be prepare to spend the day up here monitoring?

Thanks in advance.
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Old 03-28-2015, 01:21 PM   #2
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Good chance the batts discharged themselves due to internal resistance. My guess they are toast, at least the ones at 3v. You can try to charge them up, but I would monitor it as if a batt is shorted, it or the charger can overheat.

If charger can be run on 120v, you can use adapters to feed one leg of your 50a connection with an extension cord. If charger is fed by 240v, extension cord won't work.

In hindsight, next winter might disconnect pos leads from batts except for one to power bilge pumps directly.
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Old 03-28-2015, 01:54 PM   #3
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Thanks, Ski. I put a good volt meter on both banks and got 10.5 on one and 1.9 on the other.

Local battery shop says to try a manual charger to get both up above 10.5 volts and then use an automatic charger to keep from cooking them. He says automatics won't charge anything below 10.5 volts.

Sound right to you?
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Old 03-28-2015, 01:56 PM   #4
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Yea, some chargers won't even put current to a batt under a certain volt level. Old school manual chargers will.
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Old 03-28-2015, 02:10 PM   #5
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Yea, some chargers won't even put current to a batt under a certain volt level. Old school manual chargers will.


I would certainly try to charge them. You have nothing to lose at this point.
Depends how cold it got.

A weak battery will lose charge faster, the colder it is. It's a vicious cycle and ultimately, the battery can actually freeze, which breaks the plates.
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Old 03-28-2015, 02:12 PM   #6
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Angus:

You have received some good advice so far. Let me expand a bit.

You can buy a cheap automotive 6 amp charger at any auto parts store or online at Amazon for less than $50. Disconnect the leads to the 10.5 volt battery and hook it up with extension cords.

A fully discharged 8D will take more than 24 hours to recharge fully, more like 40 hours. Leave it connected as long as you can. Monitor the voltage. When it gets up to 14.5 volts disconnect and let sit for a half day. Then check the voltage. Should be somewhere near 12.5 if good, but if below 12.0 it is toast. In between ????

Yes I'll bet you had unknown parasitic loads that drew down your battery: incandescent breaker indicator lights, CO detector, ???? Next time disconnect the battery leads.

David
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Old 03-28-2015, 02:14 PM   #7
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Ouch!

The Xantrex Truecharge2 says it will accept 60 to 260 or so volts for input. Guess I need to get a manual charger to get the AGMs off their knees and then find a cable adapter that will allow me to plug the boat to 110?
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Old 03-28-2015, 02:18 PM   #8
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Angus:

You have received some good advice so far. Let me expand a bit.

You can buy a cheap automotive 6 amp charger at any auto parts store or online at Amazon for less than $50. Disconnect the leads to the 10.5 volt battery and hook it up with extension cords.

A fully discharged 8D will take more than 24 hours to recharge fully, more like 40 hours. Leave it connected as long as you can. Monitor the voltage. When it gets up to 14.5 volts disconnect and let sit for a half day. Then check the voltage. Should be somewhere near 12.5 if good, but if below 12.0 it is toast. In between ????

Yes I'll bet you had unknown parasitic loads that drew down your battery: incandescent breaker indicator lights, CO detector, ???? Next time disconnect the battery leads.

David
Thanks all. David, our posts crossed. I'll give your method a try. And will definitely pull the positive cables next year. Live and learn.
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Old 03-28-2015, 02:23 PM   #9
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I would try to find the load before next winter.

If not, you run the risk of the same thing happening, connected or not.
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Old 03-28-2015, 03:01 PM   #10
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I would try to find the load before next winter.

If not, you run the risk of the same thing happening, connected or not.
Thanks. Just curious how an external load would drain the batts if I disconnect the cable. (I've GOT to school myself on this.)
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Old 03-28-2015, 03:20 PM   #11
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How many CO detectors do you have? If they are Fireboy Xintex, each one draws 2.7 amps a day when the temp is below freezing. That can add up over the winter. There may be other items drawing power that are "hot wired" to your batteries. look at the electrical diagram for your boat for circuit panels that may have "24 hours" in the name. These usually contain items that are powered all of the time. They may require pulling fuses to depower things like your CO detectors.

Once the battery voltage gets low, it becomes more subject to freezing. Once they freeze you could have internal or external damage ruining the battery. I would be careful hooking a charger up to the battery that is only showing 1.9 volts.
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Old 03-28-2015, 03:57 PM   #12
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The top over you boat looks like an excellent place to put one or two solar panels. Even in a northern winter you will get some charge and possibly save the batteries. Make sure you get a good controller as you don't want to over charge.
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Old 03-28-2015, 05:56 PM   #13
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Ian, I think there is a good chance they will come back. As David said put the charger on. If the charger is capable you may try a conditioning or equalizing charge to blow the sulfates off the plates. About the best price for an 8d AGM is near $500 ea. So, a good try at charging is worth it.
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Old 03-28-2015, 06:01 PM   #14
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BlueYonder, I don't think any CO detector was left plugged in, but I'm sure there has to be a load somewhere.

Marty, solar is definitely on my list. The shrink wrap would have complicated things this year though.

Found this on another forum. Anyone heard of this trick? Supposedly, it's from Exide.


For those folks that use spiral-wound AGM batteries like Optima or Orbital on your boats,, you may have already discovered that they donít tolerate a real deep discharge very well.. When completely drained they wonít accept a charge and you might then assume, reasonably enough, that the battery is completely shot..

But thatís not always true, and in most cases it probably isnít. Hereís what goes onÖ. When those battery types fall below 9 or 10 internal volts they go on strike and will not take a charge by any conventional method.. But thereís a trick, not unlike a CPR rescue effort for dead batteries..

If you have a conventional lead-acid battery handy, you can connect the AGM battery to it with hard-connection cables (not jumper cables) and then hook up a battery charger to the lead-acid battery and turn the charger on..

Charging current flowing through the lead-acid battery is then accepted by the AGM battery.. Donít know why this works.. It just does.. And since these spiral-wound batteries cost around double what a conventional L-A battery does,, its ycertainly worth giving it a try before junking what appears to be a dead dog..
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Old 03-28-2015, 06:05 PM   #15
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Ian, I think there is a good chance they will come back. As David said put the charger on. If the charger is capable you may try a conditioning or equalizing charge to blow the sulfates off the plates. About the best price for an 8d AGM is near $500 ea. So, a good try at charging is worth it.
Thanks, Don. I bought a manual charger and will start on this in the morning.

$500 each!!! Counting Larry's manatee boxers, (see "Unbelievable" thread), that makes two scares I've had today.
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Old 03-28-2015, 06:11 PM   #16
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My marina does not like for people to be plugged in for the safety of everyone else from fire. I always ask them if it would be OK for me to plug in once each month for a 24 hour period. I have never been turned down yet. Once a month will keep your batteries from freezing due to low voltage. Plus it will save your batteries.
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Old 03-28-2015, 06:17 PM   #17
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Thanks. If your marina is Bohemia Bay, we were dock mates last summer.
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Old 03-28-2015, 06:26 PM   #18
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Charge them long and low. Don't try to put high amps into them.
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Old 03-28-2015, 06:41 PM   #19
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You might be able to set up a solar panel off the boat, but next to it where it could get some sun. That way it does not interfere with the shrink wrap.
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Old 03-29-2015, 08:14 AM   #20
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Just a bump to see if anyone's used this trick to recharge "dead" AGMs.

Quote:
Originally Posted by angus99 View Post


For those folks that use spiral-wound AGM batteries like Optima or Orbital on your boats,, you may have already discovered that they donít tolerate a real deep discharge very well.. When completely drained they wonít accept a charge and you might then assume, reasonably enough, that the battery is completely shot..

But thatís not always true, and in most cases it probably isnít. Hereís what goes onÖ. When those battery types fall below 9 or 10 internal volts they go on strike and will not take a charge by any conventional method.. But thereís a trick, not unlike a CPR rescue effort for dead batteries..

If you have a conventional lead-acid battery handy, you can connect the AGM battery to it with hard-connection cables (not jumper cables) and then hook up a battery charger to the lead-acid battery and turn the charger on..

Charging current flowing through the lead-acid battery is then accepted by the AGM battery.. Donít know why this works.. It just does.. And since these spiral-wound batteries cost around double what a conventional L-A battery does,, its ycertainly worth giving it a try before junking what appears to be a dead dog..
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