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handiman
Novice
Aug 30, 2010, 11:43 AM
Post #1 of 6
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Just looking for a little insight really. I have a 1995 motorhome on a Chevy P30 chassis. When I bought it two years ago it had two new 12v deep discharge batteries. One operates the engine, for starting, lights etc. The other is the "house" battery for twelve volt house lights, refrigerator, fans, etc. There is a rectifier setup that will charge both batteries when plugged into 120v service. The alternator charges both batteries while driving. The batteries will constantly go dead if the RV is left to sit for more than a week or two without being hooked up to 120v power. So I installed a knife switch type disconnect on the negative terminal for each battery. When you open this switch, the negative terminal is disconnected from the frame completely. This is the recommended procedure from an RV dealership. Their theory is if the ground is disconnected, the battery cannot drain off. But it still does. I thought they may be discharging because they were sitting on a metal frame in the vehicle, which is grounded. People will always tell you not to sit a new battery on a concrete floor, especially a damp one, or the battery will discharge. So I cut some plastic and placed it underneath both batteries. They still lose their charge. The only thing I can think of is that deep discharge batteries simply lose their charge while sitting, even if completely disconnected. When traveling, the whole setup works fine, because they are charged while driving and while parked and plugged into AC power. Am I missing something, or is this just the nature of deep discharge batteries? Any insight would be appreciated.
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Hammer Time
Ultimate Carjunky
/ Moderator
Aug 30, 2010, 12:31 PM
Post #2 of 6
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Re: RV battery drain
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Are you sure you disconnected the only ground? Many battery ground cables have more than one ground and if any of them are still hooked up, both batteries are connected through the switch so they will still drain. They make electronic control switches for RVs just for that purpose. You don't have just a simple, single battery hook up there.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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handiman
Novice
Aug 30, 2010, 1:21 PM
Post #3 of 6
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Re: RV battery drain
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I am certain there are no grounds connected when the switch is open. There is only one negative cable on each battery post. I removed that, placed the switch on the post, and connected the one cable back to the other side of the switch. There are for sure multiple wires connected to the positive posts of both batteries, but only one to the negative post. That is one reason they tell you to put the switch on the negative post. Things are a lot less cluttered.
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Hammer Time
Ultimate Carjunky
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Aug 30, 2010, 1:32 PM
Post #4 of 6
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Re: RV battery drain
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Then you have to realize that there is no possible way for the vehicle to draw power with an incomplete circuit to the battery so if your not mistaken about the ground wires, then you just have bad batteries because the vehicle can't be doing it.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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handiman
Novice
Aug 30, 2010, 2:27 PM
Post #5 of 6
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Re: RV battery drain
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Well, my question was and still is, can it be a symptom of the type of battery. These deep discharge batteries are different from regular automotive batteries in that they are designed to be able to be completely discharged and then recharged up to 350 times before going bad. Do that three or four times to a regular car battery and you are headed for the nearest Battery Warehouse or automotive supplier. But I have rechargeable batteries for other appliances that if just left lay on the bench for a couple of weeks are completely dead and must be recharged. That's why I hate rechargeable tools. Whenever you need them they always seem to be dead. So I just wondered if it is the same with the deep discharge batteries. I would think if they were bad, they wouldn't work when traveling and being used on a normal charge/discharge cycle.
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Hammer Time
Ultimate Carjunky
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Aug 30, 2010, 2:35 PM
Post #6 of 6
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Re: RV battery drain
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No, that battery is not designed to go all the way discharged 350 times. That will wipe out any battery. It's not even recommended to let it get completely discharged at all. The only difference in a deep cycle battery is it will hold up a little better to slow discharges but it's no miracle battery. No car battery should be allowed to be completely discharged at any time and any battery left connected to anything for a long period of time will discharge whether it has a parasitic draw or not. That's why boats have battery switches.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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