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Old 09-18-2016, 10:56 AM   #1
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House Battery Blues?

Hey, hoping someone can help shed some light on a won't-hold-a-charge house battery issue in my 1995 RB30 (Fresno-built) SMB. This has me pretty stumped for the moment.

Quick description of my setup:
I've got a pretty-darn-simple Sportsmobile, as far as they go (electrically, anyway), with super-low electrical current needs.

* One 12V house battery (Group 27, basic deep-cycle RV/Marine)
* No solar.
* 2-way refrigerator (uses either 120V AC or Propane to operate)
* All light fixtures LED
* No sophisticated battery charge/monitoring system, only the simple "plug into the cigarette lighter" digital charge meter sold at most Camping World locations...

( This one: )



The Issue:
After getting two years out of the house battery (that I had installed fresh/new shortly after picking up the van in July of 2014)....it was starting to not recharge so well. Wouldn't return to a very high state of charge (only about 12.4 volts, sometimes 12.5 volts), and even while charging, the meter displayed a total voltage that was still in the low 13's.

After doing some reading, I realized that I had probably shortened the lifespan of the battery dramatically by (most likely) running the battery down **too low** before recharging it. I found this chart about two months ago, and it really shed some light (for me, anyway) on how "fussy" the house battery can be, in terms of how low you can safely discharge a "deep cycle" battery and not begin to ruin it.



(Up to this point, I had relied only on the three "GREEN/YELLOW/RED" state-of-charge lights on my cheap-o plug-in voltage meter...I didn't bother to recharge the house battery back-to-full until the meter was showing either yellow or red......hadn't paid attention to the actual voltage numbers as much. So I was quite often allowing the battery to drop as low as 11.9 or 12.0.)

So it became clear I had probably damaged the battery by letting it run down too low. Off I went to pick up an exact-replacement battery.

And so now....the real puzzler:
The new battery recharges wonderfully!
Tops off at a natural resting charge of between 12.7 and 12.8, most days. Displays well into the 14's while charging.

BUT:
Within literally 1 or 2 minutes after doing so much as turning on *ONE LED LIGHTBULB*, the displayed voltage abruptly drops from 12.7 to 12.5 volts. Or 12.4 volts. Or lower. And it doesn't pop back up.

There's no way that one randomly-chosen LED fixture (among any of them in the van) can be suddenly draining that much juice from a brand-new house battery in 2 minutes. Or can it? (Perhaps by enabling some other parasitic "short" or something?)

I'm breaking out the electrician's test meter this afternoon, and verifying that indeed the displayed house voltage is correct (as shown on the cheapie voltage meter), but if it's indeed correct.....and the house battery voltage is indeed dropping that much, that fast......is a "bad battery" the most likely culprit here? Anything else that's obvious (not to me, anyway) that I should be checking?

Grateful for any advice or insight anyone can offer here.
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Old 09-18-2016, 11:15 AM   #2
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I agree, test the battery voltage on the posts just to see. It's a AGM?
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Old 09-18-2016, 11:30 AM   #3
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You should also take it to a reputable battery shop or two and have them put their load tester on it. They can tell you the exact state of the battery in a couple of minutes. It should not cost you anything. The reason I said "or two" is so that you can verify that the first shop is not trying to pull a fast one.
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Old 09-18-2016, 11:33 AM   #4
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I think you have a short somewhere, but I also think that chart is for a standard battery (as it says) and not a deep cycle. I think you shorten the life of any battery by cycling it and running it down on occasion, but a deep cell can handle a lot more abuse than that chart states.

Still, I'd find the short and go from there.

How to Find a Parasitic Battery Drain: 9 Steps

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Old 09-18-2016, 11:37 AM   #5
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Quote:
Originally Posted by daveb View Post
I agree, test the battery voltage on the posts just to see. It's a AGM?
Thanks for the replies guys.

Not an AGM, it's a standard wet-cell RV/Marine deep-cycle battery.
(Autozone Part Number: 27DP-DL)
Duralast/Marine battery - 12 months free replacement 27DP-DL at AutoZone.com - 4 reviews
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Old 09-18-2016, 11:37 AM   #6
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From what I understand, and I am going off what I have read in various places, an alternator will not return an AGM to a full state of charge. Since you have a very simple setup, it may do for you to get an inexpensive AGM charger that will plug in when you go shore power. You can charge it at home this way too. That will finish the full charging of your house battery. Alternators will do the bulk only. AGM's need to be charged periodically, and properly, if your van sits for a long period.

And I agree that you may have a short. You could test the lighting circuit to see what one light is drawing as far as amps. If it's a lot, then investigate further. LED's themselves can short and still light, drawing a good amount of power. If they aren't soldered correctly to their circuit boards, they have shorts and can still light. You may want to set up a volt meter to test your Light circuit amps and flip on each one individually to see if one is drawing more than the others.
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Old 09-18-2016, 11:47 AM   #7
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Quote:
Originally Posted by MountainBikeRoamer View Post
Thanks for the replies guys.

Not an AGM, it's a standard wet-cell RV/Marine deep-cycle battery.
(Autozone Part Number: 27DP-DL)
Duralast/Marine battery - 12 months free replacement 27DP-DL at AutoZone.com - 4 reviews
Oh hell, thought you had an AGM. That type is easy to test w/o having to pull out. Wet cell batteries require watering maintenance so I'm sure you have access to the caps. Just use a battery hydrometer and test each cell.
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Old 09-18-2016, 12:00 PM   #8
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my thoughts:

1. bad battery - as Dave says, check each cell.
2. drain - as Eric says, find it!

Not really any other options.
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Old 09-18-2016, 12:54 PM   #9
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Ok I learned a ton from reading this one simple thread. Cheers
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Old 09-18-2016, 01:20 PM   #10
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Originally Posted by Annie O View Post
Ok I learned a ton from reading this one simple thread. Cheers
Me too!
And still learning.

Question:
Anyone have any positive/negative (hah!) things to say about this harbor freight battery load tester? And if this is as useful as any other means of testing a battery for bad cells?

100 Amp 6/12V Battery Load Tester
Cen-Tech - Item#69888

6 Volt/12 Volt Battery Load Tester


>>> I'm still in the middle of making sense of whether or not my house battery is in fact sealed (and thus, not able to be tested with a battery hydrometer.)
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