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Old 12-23-2009, 11:16 AM   #1
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1999 34' Excella
Joshua , Texas
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charging 8 batteries in an RV...

I have a 34' with 8~Optima's and they are all low on voltage, around 6 volts. The Airstream has been in storage for about 9 months and not hooked up to any charger.

The on-board charger/inverter won't engage until the batteries are at 10.5 volts so using shore power is out of the question and the trailer pigtail is a very slow method to charge.

I tried connecting a 10 amp charger to the batteries, but after about 10 minutes, the cord from the charger to the batteries was getting too hot.

Short of disconnecting the batteries and charger them one-by-one or in groups of 2, what are the other options?

Any suggestions?

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Old 12-23-2009, 11:30 AM   #2
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You could have one battery that has a shorted cell dragging the others down so I think your only option is to disconnect and charge/test one at a time.

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Old 12-23-2009, 11:40 AM   #3
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Originally Posted by Dwight View Post
...Short of disconnecting the batteries and charger them one-by-one or in groups of 2, what are the other options?
well the underlying question is are ANY of the batteries salvageable IF they are at 6 volts?

the quickest solution is to purchase (or borrow) a charger/inverter that will function from zero volts up...

i think the xantrex units will do that.

IF you do use another C/C go for 80 amps or MORE in size.

connecting a solar array and charger is another option, bypassing the onboard C/C until the voltage is UP.

but i agree EACH battery needs to be tested and the weakest ones PULLED of the wiring until the others are boosted.

all of the true things that i am about to tell you are shameless lies. l.b.j.

we are here on earth to fart around. don't let anybody tell you any different. k.v.
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Old 12-23-2009, 11:55 AM   #4
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I hope that none are bad, but.....

They are only about 2 years old and my plan now is to try the charger on banks of 3 and see if that will prevent the wire from getting too hot, then back off if that doesn't work!

I believe that I had some items that were left on accidentally and that has drained them all down.

I have solar panels on the roof, but the trailer is kept under covered storage....
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Old 12-23-2009, 01:30 PM   #5
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re: " I hope that none are bad, but....." - a 12v battery pulled down to 6v is on borrowed time if not already dead.

Put a 12v light bulb in series with your 10 amp charger to help reduce currents as you try to bring the batteries up. Even with just 1 battery at a time, a resistance like this can be a good idea as AGM's will pull a lot of current that the charger may not be able to handle for very long.

Then invest in a converter or battery maintainer that will keep your batteries at top charge and apply a desulfation technique when you are not using your batteries for more than a couple of weeks. To get optimum life from your batteries, exercise them properly, recharge promptly and with appropriate vigor, and don't let them sit without a top charge for very long.
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Old 12-23-2009, 03:05 PM   #6
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Get ahold of a regular lead acid battery and hook it up parallel to the Optima. That will fool your charger into seeing a voltage above the 10.5 cutoff where most chargers shut down. If the battery is taking a charge you will know it because the battery will warm up after 30 minutes or so. If it gets really hot after an hour it has a short and should be recycled.

I'm not sure a shorted cell is the problem. That usually happens when a chunk of sulphate breaks off and fall to the bottom of the case. That's not gonna happen with a gel cell.
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Old 12-23-2009, 04:38 PM   #7
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South of the river , Minnesota
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There is more here than meets the eye. Even a crap lead acid battery will come up to 10.5 volts in a matter of seconds with a couple of amps applied.

I'm guessing that there's a fairly sizable load somewhere that isn't disconnected.

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