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Old 08-03-2008, 01:18 PM   #1
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I checked my house batteries the other day with a specific gravity probe. All the cells were either "dead" according to the specific gravity or close to it. These are NAPA deep cycle marine battiers and are 18 months old. It seems that every so often when charging with deminisions unit i've noticed very warm batteries and bubbling.

I removed the 3 batteries from the unit and took them to a NAPA store. To my supprise the desk guy tells me I can't tell if battery is good or bad by checking the cells with the gravity probe because they are "deep charge" batteries.

He palces the batteries on his unit and tells me they are all in good condition.

Any one heard of how you dom check these battery cells if not by the hydrometer (specific gravity).

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Old 08-03-2008, 01:18 PM   #2
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I checked my house batteries the other day with a specific gravity probe. All the cells were either "dead" according to the specific gravity or close to it. These are NAPA deep cycle marine battiers and are 18 months old. It seems that every so often when charging with deminisions unit i've noticed very warm batteries and bubbling.

I removed the 3 batteries from the unit and took them to a NAPA store. To my supprise the desk guy tells me I can't tell if battery is good or bad by checking the cells with the gravity probe because they are "deep charge" batteries.

He palces the batteries on his unit and tells me they are all in good condition.

Any one heard of how you dom check these battery cells if not by the hydrometer (specific gravity).

Journey 07 36G
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Old 08-03-2008, 01:55 PM   #3
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" To my supprise the desk guy tells me I can't tell if battery is good or bad by checking the cells with the gravity probe because they are "deep charge" batteries. "
I don't think I have ever heard that one before. I found a bad cell on one of my deep cycles with a hydrometer (specific gravity)
causing both batteries to go dead. I doubt if you have 3 bad batteries but only one that has a bad cell causing the rest to go bad. Also causing the charging problems.
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Old 08-03-2008, 03:00 PM   #4
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Hydrometers work just fine on deep cycle batteries. I check mine that way all the time.
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Old 08-03-2008, 05:31 PM   #5
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Using a hydrometer, can the 6 cells vary any and the battery still be okay? Or do all the cells need to read exactly the same? I use the one that floats 1-4 balls.
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Old 08-03-2008, 06:17 PM   #6
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by jk_and_dog:
I checked my house batteries the other day with a specific gravity probe. All the cells were either "dead" according to the specific gravity or close to it. These are NAPA deep cycle marine battiers and are 18 months old. It seems that every so often when charging with deminisions unit i've noticed very warm batteries and bubbling.

I removed the 3 batteries from the unit and took them to a NAPA store. To my supprise the desk guy tells me I can't tell if battery is good or bad by checking the cells with the gravity probe because they are "deep charge" batteries.

He palces the batteries on his unit and tells me they are all in good condition.

Any one heard of how you dom check these battery cells if not by the hydrometer (specific gravity).

Journey 07 36G </div></BLOCKQUOTE>Bzzz..gong.. The NAPA guy doesn't quite have his stuff together.

Depending on the battery application (cranking or deep discharge) the specific gravity might vary a bit from battery type to battery type, but within a battery, all cells should read fairly close to one another. If not, you have a wonky cell(s.) An equalization cycle might restore the cell, or not.

The bubbling and gassing you observe could be the Dimensions going through its conditioning/equalization cycle (every tenth time it charges I believe), or it could indicate a bad cell(s) in one of the batteries.

The primary difference between starting and deep cycle batteries is the thickness of the lead plates. Starting batteries have a bunch of thin plates and deep cycle have fewer but thicker plates. Chemically, they are both the same.
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Old 08-04-2008, 08:45 AM   #7
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Specific gravity will tell you about the battery state of charge and not its health.

There is no real need for hydrometry with modern RV batteries as voltage will also tell you about state of charge and not incur the hazards of dealing with a caustic acid nor suffer the risk of cross contamination. Both voltage and specific gravity measures require proper interpretation. Both require resting batteries with well mixed electrolyte and proper temperatures for useful measurements.

As for the NAPA dude, keep in mind that there really isn't any such thing as a true "deep cycle" battery for RV's (or that you would be likely to find in his store). The differences between the typical SLI and RV batteries are really rather minor and you don't run any of them down more than 50% for best battery life.

To determine the health of a battery, the time tested method is a load test. Put a load on the battery and see how it responds and how long it lasts. (see smartgauge for an example of a meter that uses this idea)

A newer (since the 90's) and less destructive health test is conductivity testing. Some of the modern battery chargers have simple versions of this method in them but a good commercial test unit can cost towards $1,000.

State of Charge is not the same thing as State of Health!
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Old 08-04-2008, 12:49 PM   #8
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by BryanL:
Specific gravity will tell you about the battery state of charge and not its health.

There is no real need for hydrometry with modern RV batteries as voltage will also tell you about state of charge and not incur the hazards of dealing with a caustic acid nor suffer the risk of cross contamination. Both voltage and specific gravity measures require proper interpretation. Both require resting batteries with well mixed electrolyte and proper temperatures for useful measurements.--snip--
State of Charge is not the same thing as State of Health! </div></BLOCKQUOTE>Measuring SG is still the best way to determine the state of charge for each cell, and as you point out it is not 'good/bad' test per se. However, if the SG of one cell or cells is lower than its neighbors, you certainly can infer a battery problem. Voltage measurements are much less useful since all voltage charts (and they vary a tenth of a volt here and there) assume a battery at rest for 24 hours so results accuracy is much more problematic.

I don't believe a 24 hour rest period is that essential for checking SG. You make sure the battery is fully charged (in float state), knock off the surface charge with a ~20 amp load for about three minutes, and check away.

The hydrometer is alive and well.

The load test is what shops generally use to determine if the battery can produce at its rated capacity.
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Old 08-05-2008, 10:28 AM   #9
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">The hydrometer is alive and well. </div></BLOCKQUOTE>
Yes, I know. Old habits die hard and myths from days of yore have a life of their own even as technology has superseded, them.

The caveats about voltage do apply to specific gravity and for much the same reasons. You won't often find much information about this, though. Take a look, for instance, at Trojan's battery maintenance flier (PDF) - same procedure for both methods (temperature compensation only in this case). Look around and you'll find how stratification of electrolyte and other problems can make for measurement interpretation problems.

The fact is that for today's RV batteries and the small banks they use, the risks from measuring specific gravity don't really get you anything you can't get from less intrusive and much safer means such as using a modern DVM with sufficient precision.

Also note that the load test is destructive. The conductivity test isn't and can provide equivalent results. See BatteryUniversity.com and their Cadex sponsor.
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Old 08-05-2008, 12:53 PM   #10
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by BryanL:
--snip--Also note that the load test is destructive. The conductivity test isn't and can provide equivalent results. See BatteryUniversity.com and their Cadex sponsor. </div></BLOCKQUOTE>A load test is no more destructive than a typical boondocking session when you are running on batteries for hours/days.

In a flooded cell battery, the hydrometer is the real deal.
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Old 08-05-2008, 05:12 PM   #11
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Hi All,

http://www.smartgauge.co.uk/

Without doubt, THE' most comprehensive description of lead acid battery technology I have ever seen!

If you really want to know what's up with your batteries, why they work sometimes and not others, this web site has the answers for you. A little deep at times but so thorough.

Their products look very good also, except for the current rating of the tie contactor. For RV start applications, a much higher current rating would be nice to have, otherwise, it should work very well for RV's. One of the Product pages says "Available for systems up to 600 amps charge capability" but they don't show a contactor that is rated for 600 Amps. Maybe they just parallel three 200 Amp. contactors.

Thanks to BryanL for pointing us to this site!
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Old 08-06-2008, 08:51 AM   #12
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">A load test is no more destructive than a typical boondocking session when you are running on batteries for hours/days. </div></BLOCKQUOTE>
a proper load test will take your battery down to near zero state of charge. That is much more destructive to battery life than proper use that only discharges the battery to 50% SoC.

Yes, you can get away with totally draining the battery a time or two but that is a destructive practice and not good for optimum battery life.

Hydrometry is no skin of my nose but I do wonder about religious zealotry for its use. What I do support is that folks carefully consider the hazards involved and the benefits of the alternative for the goals the seek.
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