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Old 11-16-2020, 08:30 PM   #1
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Brand: Thor Motor Coach
State: Wisconsin
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THOR #21256
House Batteries Rapidly Draining

I've had my RV plugged in to shore power at home for probably a month now. Its a Thor Quantum RC25 since our last camping trip. Everything seemed fine on that last trip while driving, and generally we're hooked up to shore power always at the camp site. I went to disconnect from power and found the house batteries were completely dead. So I used my trickle charger to charge them up. I got the RV to power up on batteries, but the battery meter was showing a sharp power drop over time with the power on. Any idea on what might be happening. When I checked the voltage on both marine batteries, one was only showing 10.8v which seemed kind low, and the other about 11.2v.
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Old 11-16-2020, 08:39 PM   #2
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Originally Posted by Ovation12s View Post
I've had my RV plugged in to shore power at home for probably a month now. Its a Thor Quantum RC25 since our last camping trip. Everything seemed fine on that last trip while driving, and generally we're hooked up to shore power always at the camp site. I went to disconnect from power and found the house batteries were completely dead. So I used my trickle charger to charge them up. I got the RV to power up on batteries, but the battery meter was showing a sharp power drop over time with the power on. Any idea on what might be happening. When I checked the voltage on both marine batteries, one was only showing 10.8v which seemed kind low, and the other about 11.2v.
One of your batteries is shot and perhaps the other as well

Load test them

check and be sure they are charging on the converter when plugged in with your VOM
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Old 11-16-2020, 08:42 PM   #3
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Lots of possibilities here.....

First... Are you sure your Use / Store Switch was in the "USE" position when you were plugged into shore power? If not, your batteries were never charging and discharged over the last month when you thought they were charging. If you are in the "USE" position check the output of your Converter / Charger. There is a breaker for the unit itself but also regular fuses to protect against reverse polarity.

Second..... How old are your batteries? They could be at the point of needing replaced if they won't charge up and hold a charge BUT a trickle charger is not going to charge a deeply discharged deep cycle battery.

Third.... If they are wet batteries, when was the last time you checked to make sure the cells were adequately covered?
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Old 11-16-2020, 09:03 PM   #4
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10.8 to 11.2 volts isn't just kind of low, it is dead! Replace them and then follow the suggestions above to make sure they are charging.

With shore power connected, the converter working and the use/store switch in use, then the batteries should read in the 13s.

David
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Old 11-16-2020, 10:08 PM   #5
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Its a 2019 RC25. I bought it used, so not exactly sure, but I guess they could be 2 to 2-1/2 years old which doesn't seem like much. Also we haven't used it off shore power much at all. Anyone know where the power converter might be on an RC25? Wondering if the fuse may have blown there.
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Old 11-16-2020, 10:11 PM   #6
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Also the RC25 doesn't have a Use/Store or at least it's not labeled that way and it doesn't appear to work that way. It just says Main Power with a red light that is always on with shore power and needs to be turned on with accessory batteries.
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Old 11-16-2020, 10:34 PM   #7
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Originally Posted by Ovation12s View Post
Its a 2019 RC25. I bought it used, so not exactly sure, but I guess they could be 2 to 2-1/2 years old which doesn't seem like much. Also we haven't used it off shore power much at all. Anyone know where the power converter might be on an RC25? Wondering if the fuse may have blown there.


The batteries may not last long if you donít add water regularly- especially if you store them on a charger. Also the previous owner or even the dealer when it was new may have abused or neglected them. The factory batteries are somewhat high maintenance . The test is not age but voltage. As above yours are dead and almost certainly cannot be revived. Treated well flooded batteries should last about 5 years in my experience. Many brand new coaches need new batteries if the unit was on the lot for more than a short time. Mine suffered catastrophic failure on my very first trip and the RV manufacturer reimbursed me with no fuss. The switch you describe is the one in question.
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Old 11-16-2020, 11:35 PM   #8
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Originally Posted by Ovation12s View Post
Also the RC25 doesn't have a Use/Store or at least it's not labeled that way and it doesn't appear to work that way. It just says Main Power with a red light that is always on with shore power and needs to be turned on with accessory batteries.

The red light for that switch will always be ON when you are plugged into shore power.... even if the switch is in the STORE or OFF position. That's why some people think it is in the USE or ON position even though the batteries are really disconnected and therefore will not be charging.

Depending on what type of switch you have you can do the following:

- Unplug your shore power

- If the switch is in the USE or ON position the red light will still be on (if you have enough battery power)

- If the red light is off after unplugging shore power, the switch is in the STORE or OFF position and the batteries are disconnected and not being charged. Hit the switch and the red light should come on

- Plug in your shower power

- Measure your battery voltage.... you should be seeing over 13V if the Converter is charging them (and they are not fried).
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Old 11-16-2020, 11:45 PM   #9
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That switch's operational design seems confusing...
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Old 11-19-2020, 05:38 PM   #10
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I have enough power in the batteries after attempting a recharge to check what you're saying. If AC is plugged in, and the power is on, when I disconnect the power the power stays on. If I turn off the power while its not connected to AC, then when I plug it in to AC it does not go on until I flip the switch. If AC is unplugged, and I turn the power switch on, then plug in AC, it remains on. I don't see this working in anyway like the USE/STORE switch I see everyone reference. It does not appear to exist on a Thor Quantum RC25.
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Old 11-20-2020, 03:56 PM   #11
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So I'm someone who isn't afraid to admit when he's wrong, and I want people to know the facts more than I want to hide my own stupidity. My test was flawed, didn't realize the other end of the shore power wasn't plugged in. After rectifying, I checked for charging and I was well over 13 volts to the battery. So the converter was doing it's job. I also got some info from Thor directly, that helped me identify where the converter was (under the fuse box), and the fact that there was a fuse inline at the battery. I also added distilled water to the cells. I checked the power switch with the shore power disconnected, made sure it was on, reconnected shore power and let it charge over night. It all looks good now. I also re-checked the Use/Store paradigm, and its seems to work as described even though it doesn't say use/store. As for the batteries being bad, I recall as a kid that my dad would use a lead acid cell tester, a hydrometer. It looks like syringe, basically you suck up some water from the cell and you check if the cell is bad based on the markings. If any of the cells are bad, game over, but rather than randomly guessing and throwing out batteries, this seems more scientific, and they only cost about $15 on Amazon. Probably worth the investment.
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Old 11-20-2020, 04:34 PM   #12
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Originally Posted by Ovation12s View Post
So I'm someone who isn't afraid to admit when he's wrong, and I want people to know the facts more than I want to hide my own stupidity. My test was flawed, didn't realize the other end of the shore power wasn't plugged in. After rectifying, I checked for charging and I was well over 13 volts to the battery. So the converter was doing it's job. I also got some info from Thor directly, that helped me identify where the converter was (under the fuse box), and the fact that there was a fuse inline at the battery. I also added distilled water to the cells. I checked the power switch with the shore power disconnected, made sure it was on, reconnected shore power and let it charge over night. It all looks good now. I also re-checked the Use/Store paradigm, and its seems to work as described even though it doesn't say use/store. As for the batteries being bad, I recall as a kid that my dad would use a lead acid cell tester, a hydrometer. It looks like syringe, basically you suck up some water from the cell and you check if the cell is bad based on the markings. If any of the cells are bad, game over, but rather than randomly guessing and throwing out batteries, this seems more scientific, and they only cost about $15 on Amazon. Probably worth the investment.
Also be sure the dealer didn't cheap out & put marine hybrid batteries in the coach. If there's CCA, CA, or MCA followed by a number listed on the battery tops you have cranking batteries not true deep cycle batteries. These batteries are not designed for rv use where constantly charging/discharging takes place.
Testing your batteries is a good idea. If they've been completely dead with low water levels then they may charge but not stay charged & if so their lifespan has been shortened considerably.
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Old 11-20-2020, 06:40 PM   #13
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Originally Posted by Ovation12s View Post
As for the batteries being bad, I recall as a kid that my dad would use a lead acid cell tester, a hydrometer. It looks like syringe, basically you suck up some water from the cell and you check if the cell is bad based on the markings. If any of the cells are bad, game over, but rather than randomly guessing and throwing out batteries, this seems more scientific, and they only cost about $15 on Amazon. Probably worth the investment.
A hydrometer is the gold standard for flooded battery condition. Tables for a graduated hydrometer are available on line.
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Old 11-25-2020, 07:57 PM   #14
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Originally Posted by Ovation12s View Post
I've had my RV plugged in to shore power at home for probably a month now. Its a Thor Quantum RC25 since our last camping trip. Everything seemed fine on that last trip while driving, and generally we're hooked up to shore power always at the camp site. I went to disconnect from power and found the house batteries were completely dead. So I used my trickle charger to charge them up. I got the RV to power up on batteries, but the battery meter was showing a sharp power drop over time with the power on. Any idea on what might be happening. When I checked the voltage on both marine batteries, one was only showing 10.8v which seemed kind low, and the other about 11.2v.
We were having a very similar problem. We went through all of the troubleshooting steps that others have posted here. When all of that failed we took it in, and the problem turned out to be a bad inverter that had to be replaced.
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