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Old 10-12-2019, 05:48 PM   #1
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Dead house batteries

I made a rookie mistake and forgot to turn off my house batteries, they were down to 2.9 volts. My question is how long will it take shore power to recharge them
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Old 10-12-2019, 06:30 PM   #2
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Maybe never. Just start charging and see if they hold a charge.
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Old 10-12-2019, 06:52 PM   #3
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Start the engine the RV has a 100 amp alternator. It will charge the house batteries quicker.
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Old 10-12-2019, 07:17 PM   #4
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Start the engine the RV has a 100 amp alternator. It will charge the house batteries quicker.
Yes if you want to leave the engine on for 8 hours or more. Better to try using the built in converter. Also, many battery isolators won't allow connection if the one side is below a certain threshold voltage.
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Old 10-12-2019, 10:59 PM   #5
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Deleted. Replied to wrong thread.
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Old 10-12-2019, 11:04 PM   #6
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Before you replace them, try charging for 15 minutes or so on the engine/alternator. Some chargers will not charge a battery that is below a certain point. The alternator is pumping out power either way and might kick the battery up enough the charger can then take over if you try it again. Nothing to loose at this point but a little time.

Unless they are sealed, I would check the water level after charging (assuming they charge). You probably shortened their life either way, but they may not be toast yet.
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Old 10-12-2019, 11:10 PM   #7
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Before you replace them, try charging for 15 minutes or so on the engine/alternator. Some chargers will not charge a battery that is below a certain point. The alternator is pumping out power either way and might kick the battery up enough the charger can then take over if you try it again. Nothing to loose at this point but a little time.

Unless they are sealed, I would check the water level after charging (assuming they charge). You probably shortened their life either way, but they may not be toast yet.


X2 I had left lights on and killed the battery on my TT let battery charger on all night no good. Drove 6 hours to my campsite. By the time I got there I forgot the battery had been dead when I unhooked. Used the power jack barely had the juice but got job done. Next morning converter finished the job batteries back to full
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Old 10-12-2019, 11:13 PM   #8
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The problem you are going to find that even getting the batteries charged to full, You have lost a LOT of capacity. The longer they were down at 2.9V, the worse it will be since sulfation is a combination of time left discharged vs voltage. Sulfation kills your capacity.
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Old 10-13-2019, 06:59 PM   #9
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The problem you are going to find that even getting the batteries charged to full, You have lost a LOT of capacity. The longer they were down at 2.9V, the worse it will be since sulfation is a combination of time left discharged vs voltage. Sulfation kills your capacity.
Perhaps I'm more of an optimist. If the batteries are relatively new, and they were are recharged with minimal delay, I believe that much of the capacity can be recovered. Sulfation is a battery killer but it's the hard sulfate that forms when a discharged battery sits for longer times that is the culprit. If a battery is recharged before this hardened sulfate forms, and is converted back into usable components one can often dodge a bullet.

Only way to know is to charge for a day or two and then test Specific Gravity. Then using temperature corrected readings compare with expected SG for a fully charged battery.

I agree with babcock, the longer they sit at low voltage the less you'll recover.
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