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Old 08-08-2013, 06:43 PM   #1
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How long will starting batt's last when swithched off?

Newby here.

I have a disconect swith in the engine compartment, when swithed off there should be no parasitic drain on the starting batteries. Any ideas on how long I can store the rig and still get it started?

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Old 08-08-2013, 08:09 PM   #2
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How long will battery hold charge

If there is NO parasitc drain, including the battery installed, not sitting on concrete (which can drain a battery), then the time will depend somewhat on the age, condition and original quality of the battery. If you use nothing but distilled water to top the battery off, to reduce the calcium in the battery fluid, it would help. You can be pretty sure that with a strong battery you will get 90 days, maybe even 120 days. After that it becomes a game of luck -- with luck it might even last 6 to 9 months, but without a "top off charge" you are in the range of "who knows" -- individual batteries might hold a charge longer, but don't count on it.

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Old 08-09-2013, 04:56 PM   #3
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I would be shocked if there were no parasitic drain even with the shut off. Several items on my coach and chasis are routed around the shut offs (CO detector, radio memory, ECM, etc.).
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Old 08-09-2013, 05:13 PM   #4
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Hi franknslots,
A battery, in storage, will loose 1 to 3% of the battery's power each month of storage. In a motor coach, there will almost always be some parasite drain.
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Old 08-09-2013, 06:09 PM   #5
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Pull a ground cable off to be sure there's no parasite drain. The battery in my car that I leave when we are RVing for 3 1/2 month starts my stay at home car fine, and I don't disconnect the battery.
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Old 08-09-2013, 10:21 PM   #6
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No one can say how long. I left my car for two weeks and it wouldn't start. My 1990 Triple E sat for 7 months through a dang cold Canadian prairies winter outside with the battery disconnected via the switch in the coach, and it started like it was a brand new car. A good battery should last for quite a long time.... or it may not.
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Old 08-10-2013, 10:28 AM   #7
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How long will batteries hold charge

There is another issue to consider. If you don't take special care to "pickle" the engine for longer term storage, then leaving the coach (and the generator engine if you have one) without starting it for over 60 days will cause rust to start forming on the cylinder walls and in the crankcase area of the engine. This might be worse in a "sea side" environment and better in a desert environment. Most of the owner's handbooks that I have seen suggest that you start both engines every 30 days during the off season to keep the engines in good condition. Since you would want to run the engines long enough to bring them up to operating temperature, in order to boil off the water in the oil that starting creates, you will charge the batteries when you do the maintenance run of the engines.
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Old 08-10-2013, 02:40 PM   #8
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Besides parasitic drains being present when wires are connected, there can be a parasitic drain across the top of the battery. Dust, dirt, debris are all conductors and can cause current to flow ever so slowly across the battery top. If you presently have a dirty battery top, use a volt-ohm meter in the amp position and touch the probes to only the case near each of the posts.

So, clean the batteries regularly besides disconnecting them. If you use a disconnect switch that you install you can isolate all RV parasitic but be prepared if you have computers that you may have to reload software.
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Old 08-11-2013, 11:30 AM   #9
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Has anyone tried one of the chargers that plugs into cig lighter as a trickle charge
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Old 08-11-2013, 12:48 PM   #10
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including the battery installed, not sitting on concrete (which can drain a battery)
Might be somewhat outdated advice.

Has anyone tried one of the chargers that plugs into cig lighter as a trickle charge
Most are too small to do a lot of good but do help - provided the lighter socket is live when the ignition key is removed.

If you have a way to keep the house battery charged, then adding a Trik-l-start will solve the chassis battery problem
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Old 08-11-2013, 02:32 PM   #11
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I got tired of chasing all the issues with systems that charge the chassis battery when the house batteries get "full". of course when the house batteries degrade and you take into account the voltage drop across some of those follower chargers the chassis battery doesn't get much.

I just bought a schumaker trickle charger, mounted to the inside of the engine compartment and tied it in to one of the 115 outlets that's NOT on the inverter when not plugged in (that way you don't burn house batteries charging chassis batteries).

However, if the tops of the batteries are clean and the ground disconnected, there's an easy way to calculate the amount of time the batteries should be viable. There should be in the manufacturer's specs a listing for internal resistance and a self-discharge rate. If you know about how many amps the starter motor draws, then you can calculate when the drop across the internal resistance pulls the batter voltage down below the point where the ECU will reset. At that point, you're done.

Practically though, you really only need enough juice to fire up the generator first. Then, once that is running, tie the house batteries to the chassis batteries and most of the time it will start.

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