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Old 05-13-2019, 08:44 PM   #1
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Join Date: Dec 2018
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Chassis Batteries Draining/Not Charging

I was having a problem with my chassis batteries draining while on shore power and/or generator. I thought the batteries were bad, they would charge, but as soon as I tried starting engine they would drop and not start it. If I jumped it, it would fire up.
So I replaced them with ones that met the specs in manual(Commercial 950 cca vs the Marine 650 cca that were in it, I think the last owner swapped them out), I charged them fully before hooking them up. Engine started right up. I drove 2 hours, parked and shut it off, ran gen for a few hours while I waited to drive again. It started right up again, thought my problem was solved. Got to next location with no shore power, started gen, ran it for about 24 hours until I got shore power for about 8 hours. Went to start gen, not enough juice. Jumped started it first try. Put charger on batteries, they were 12.1 volts and read 50%.

So I guess my question is what could be draining them or why aren't they charging with shore power or Gen?

Thanks in Advance

Bob & Terri Prince
2009 Holiday Rambler Imperial Bali IV LE
Cummins ISM 500
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Old 05-13-2019, 08:57 PM   #2
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If it were our '06 Dynasty, I would suspect the Big Boy device that ties the two battery banks together when charging energy is available. They can be troublesome, at times. Another common device that accomplishes the same purpose in many motorhomes is a BIRD (Bi-directional Isolator Relay Delay) unit. In either case, if the device is not working properly it will not tie the two batteries together and the chassis battery is usually the one that loses the charging battle.

Jim & Angie, Boise, ID
2006 Monaco Dynasty Countess III
2017 GMC Acadia Denali
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Old 05-14-2019, 07:38 AM   #3
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having the same problem

Bob, this is what I have discovered thusfar in my attempts to resolve this issue: in my coach (2007 Monaco Lapalma) I have a power inverter/charger that delivers power to the coach battery bank, and I have a second charger that is supposed to deliver power to the chasis battery bank. I think I have determined in my case that a previous owner incorrectly connected both chargers to the coach battery bank. I offer this information in case you do not have one of the previously mentioned devices that allow one charger to do all batteries. Good luck.
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Old 05-14-2019, 08:34 AM   #4
Join Date: Aug 2017
Location: Victoria BC
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I would suspect a parasitic draw somewhere on the chassis side of the 12 volt system. New batteries should be able to keep a charge and start the gen/motor without issue even if not charging, when left alone for even a couple of days. Something is pulling down your batteries while at supposed rest and a small trickle charger isn't enough to combat this draw.

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Old 05-14-2019, 08:59 AM   #5
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If your generator is running on the chassis batteries, and the generator doesn't have its own charging system ( many don't ), that will run down your chassis battery, if the isolation system ( BIRD, BIG BOY ) isn't working.

You need to figure out why the chassis battery isn't being charged While on shore/generator power.
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Old 05-14-2019, 10:06 AM   #6
Join Date: Feb 2017
Location: Beaumont, TX
Posts: 69
In addition to whats already posted, check your storage bays for lights that may have been left on. Also make sure you key ignition is fully in the off position and not accessory which happened to someone else.

I agree that one of the battery combiner/isolator components may be bad. Good knowledge of multimeter to troubleshoot or call electrician.
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Old 05-14-2019, 10:00 PM   #7
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Thanks everyone. I very seldom go without shore power, besides when driving. With old batteries I just kept a separate maintainer on after first time I had an issue. That seemed to work, when it didn't anymore is when I changed batteries.

I am going try turning kill switch to chassis batts and monitor the volts over a day or so. If that keeps them from draining, then I will keep maintainer on them until I am ready to start engine or gen.

I will check the relay in run box and let y'all know.
Thanks again

Bob & Terri Prince
2009 Holiday Rambler Imperial Bali IV LE
Cummins ISM 500
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batteries, charging, chassis

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