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Old 01-23-2014, 11:26 PM   #1
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Are my house batteries shot?

Looking for a little knowledge and assistance from you experts around here, so please chime in if you can educate a newbie here! I have had our Class C Sunseeker plugged in to shore power for the last week here at home. It has two 12-volt deep cycle batteries connected together (Positive-to-positive-to-house, negative-to-negative-to-house). It has sat idle for the last week, no use, nothing but the frige running inside. I unplugged it today for about a half hour to let the batteries rest, then put the multi-meter on both batteries (without disconnecting from each other) and they both fluctuate between 12.1 and 12.13 volts. The batteries look pretty new but I don't know the exact age. When plugged in to shore power the batteries actually read closer to 12.3 or 12.4, but when unplugged and allowed to rest they read 12.1 to 12.13.

Question 1 - From what I've read online, a 12-volt battery should have a resting voltage of around 12.4, and a reading of 12.1 means they are about 50% spent. Is that understanding correct?

Question 2 - When plugged in to shore power, do the house batteries charge back up as well or does the RV need to actually be running (driving down the road) to recharge?

Question 3 - The batteries are the maintenance free type. If they aren't able to go higher than 12.1 volts after being plugged in to shore power for an entire week, do they need to be replaced or is there something I can do to bring the charging capacity back up to the 12.4 level (i.e. add distilled water)?

Thanks in advance for any help you vets can provide to the new guy around here. I greatly appreciate it!

Scott
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Old 01-24-2014, 05:39 PM   #2
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Quote:
Originally Posted by treeguy100 View Post
Looking for a little knowledge and assistance from you experts around here, so please chime in if you can educate a newbie here! I have had our Class C Sunseeker plugged in to shore power for the last week here at home. It has two 12-volt deep cycle batteries connected together (Positive-to-positive-to-house, negative-to-negative-to-house). It has sat idle for the last week, no use, nothing but the frige running inside. I unplugged it today for about a half hour to let the batteries rest, then put the multi-meter on both batteries (without disconnecting from each other) and they both fluctuate between 12.1 and 12.13 volts. The batteries look pretty new but I don't know the exact age. When plugged in to shore power the batteries actually read closer to 12.3 or 12.4, but when unplugged and allowed to rest they read 12.1 to 12.13.

Question 1 - From what I've read online, a 12-volt battery should have a resting voltage of around 12.4, and a reading of 12.1 means they are about 50% spent. Is that understanding correct?

Question 2 - When plugged in to shore power, do the house batteries charge back up as well or does the RV need to actually be running (driving down the road) to recharge?

Question 3 - The batteries are the maintenance free type. If they aren't able to go higher than 12.1 volts after being plugged in to shore power for an entire week, do they need to be replaced or is there something I can do to bring the charging capacity back up to the 12.4 level (i.e. add distilled water)?

Thanks in advance for any help you vets can provide to the new guy around here. I greatly appreciate it!

Scott
First off, the chargers that are stock with most RVs may not charge at the right voltage thus under or over charging the battery. So it's important to monitor the fluid level in the cells. If you can't open the caps to verify the fluid level inside the cells, then your converter may have boiled the fluid off. If so, the batteries are shot.

Check the open circuit output voltage of the charger. It should be at least 12.7 - 13 VDC. If you are only getting 12.4v, the converter is under charging the batteries. Your charger is goofy, and batteries may be shot. If your voltage goes from 12.4 (when connected to batteries) to 13+VDC (when disconnected) then you surely have bad battery(s).

Check the house battery voltage with the RV running. You should see 13+ VDC at the batteries.

You can get a rough idea of the battery state of charge using voltage. The best way is to measure the specific gravity using a good quality tester.


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Old 01-24-2014, 05:48 PM   #3
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Sounds like you need to install a desulphator across your batteries to blast off caked sulphates on your plates. This will keep those batteries form taking a full charge.


I use: Car Truck motorhome Caravan Battery Desulfator Desulphator 6 or 12 Batteries | eBay

This unit will charge up; then blast the batteries with a 15+ volt shock every few hours to knock off any built up plate contamination.
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Old 01-24-2014, 06:16 PM   #4
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Question 1 - From what I've read online, a 12-volt battery should have a resting voltage of around 12.4, and a reading of 12.1 means they are about 50% spent. Is that understanding correct?

I would expect to see 12.6 or 12.7 but 12.1 is around 50%

Question 2 - When plugged in to shore power, do the house batteries charge back up as well or does the RV need to actually be running (driving down the road) to recharge?

The battery should charge when connected to shore power.

Question 3 - The batteries are the maintenance free type. If they aren't able to go higher than 12.1 volts after being plugged in to shore power for an entire week, do they need to be replaced or is there something I can do to bring the charging capacity back up to the 12.4 level (i.e. add distilled water)?

To soon to tell.
It could be the charger is not running or could be bad battery, You may not have power to the charger. You need to do more checking. Also what is the battery voltage with the charger is running on shore power?.
Also you may only have one bad battery.
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Old 01-24-2014, 06:52 PM   #5
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Pry the caps off, if you can, then check the water level to the lower rim, about 3/4 inch down. If it really looks like the desert, the batteries are probably shot. If they have water in them, invest in a battery hydrometer. They should read in the green (12.50) and most important they should be all the same. If not, you have a bad cell, replace both batteries. If they are older, say 3 or more years replace them. My charger over charged mine before I realized it. Good Luck. Be carefully with the hydrometer, it will have acid in it!
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Old 01-24-2014, 07:38 PM   #6
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Resting voltage should typically be around 12.7 to 12.8 when completely disconnected. When plugged in it has to be at 13.2-13.5 after it is completely charged, or you charger is not working right. Something is amiss with your system, probably.

I would suggest pulling the batteries and taking them to a battery shop to test, and if they are okay, I would replace the converter/charger with a PDI unit of appropriate size for your rig.
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