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Old 12-31-2007, 11:55 AM   #1
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When my batteries are fully charged and float charging the voltage reads 13.4 - 13.6.

However, once I disconnect shore power and start inverting, it drops to 12.4 - 12.5 immediately. Is this normal? One guess is that the batteries are under immediate load inverting and will drop somewhat.

I have checked the water regularly and replenished w/distilled. The batteries are 1.25 years old. I have not checked w/a hydrometer but, I don't believe I have been that hard on them.

Should I equalize them? This has been a hot topic in the past. Some say to do it every 6 months, others say you never need to do it. Given that I am a part timer it is about time for me to equalize. My Xantrex system does it for me automatically. Any advice? Naysayers? Other input.
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Old 12-31-2007, 11:55 AM   #2
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When my batteries are fully charged and float charging the voltage reads 13.4 - 13.6.

However, once I disconnect shore power and start inverting, it drops to 12.4 - 12.5 immediately. Is this normal? One guess is that the batteries are under immediate load inverting and will drop somewhat.

I have checked the water regularly and replenished w/distilled. The batteries are 1.25 years old. I have not checked w/a hydrometer but, I don't believe I have been that hard on them.

Should I equalize them? This has been a hot topic in the past. Some say to do it every 6 months, others say you never need to do it. Given that I am a part timer it is about time for me to equalize. My Xantrex system does it for me automatically. Any advice? Naysayers? Other input.
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Old 12-31-2007, 12:02 PM   #3
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Hi Scott,
12.4-12.5 is not the problem. How long to they last before getting to 12.0 to 12.2? If they still last a couple of days or more, keep on keeping on.

It does sound like this is the beginning of the end for your batteries.
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Old 12-31-2007, 12:15 PM   #4
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What voltage can the batteries drop to before they can't be used for 12v appliances or inversion to A/C?

My autogen start was defaulted to 11.4v before it kicked on automatically.
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Old 12-31-2007, 12:48 PM   #5
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Your inverter will shut down at 10v, however a battery is considered completely discharged at 11.8v.

It's difficult to determine the true state of our batteries with the onboard equipment.

This may not be exactly right, but it's my understanding of how to measure a fully charged battery's voltage.

After a battery is charged, it needs to sit for a period of time with no load connected for the surface charge to dissipate, then a true voltage reading can be taken.

If you're going to Tampa I recommend talking to John Palmer http://www.jolynenterprises.com/, if he is there, as John knows all this stuff.
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Old 12-31-2007, 02:06 PM   #6
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11.8V is needed for the refer control board. 12.1 or 12.2V is about 50% and, on average, that is as low as you should take a battery.
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Old 01-01-2008, 07:34 AM   #7
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Here is something I found once that I refer to...

How can you tell if a battery is fully charged?
The only true way to tell if a battery is fully charged is by using a good voltmeter to determine the open circuit voltage (OCV). Accessible flooded type batteries can also use a hydrometer.
Charge % Digital Voltmeter Open Circuit Voltage (OCV)
Flooded Gel AGM
100% 12.80-12.60 12.95-12.85 12.90-12.80
75% 12.40 12.65 12.60
50% 12.20 12.35 12.30
25% 12.00 12.00 12.00
0% 11.80 11.80 11.80
Divide the above values in half for 6 volt batteries or by six to determine cell voltage. The TRUE OCV of a battery can ONLY be measured after the battery has been removed from the charge or discharge load for 24 hours.
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Old 01-01-2008, 12:09 PM   #8
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Taking a voltage reading is not the best way to determine the condition of batteries. But if you check them with voltage do this. Charge the batteries until they are fully charged and then disconnect from shorepower. Press the Store switch or whatever it is called in your motorhome to disconnect 12 volts from everything. Wait at least two hours and take a voltage reading directly on the batteries with a good digital voltmeter. It should read 12.7 volts. If it is less your batteries are getting weak. (Taking a voltage reading with a load on the batteries will always give an incorrect reading.)

Equalizing is a way to make the cells "equal" to get more life out of batteries. To determine if your batteries will benefit from equalizing fully charge them and then let them sit a couple of hours with no load on them. Use a hydrometer and take reading from all of the cells. If some of the cells are lower than others equalizing will help bring the low cells up and make them "equal" to the other cells.

If you often drain your batteries below 50% they may need to be equalized every six months. If you are connected to shore power most of the time and seldom drain the batteries more than 20% they will probably never need to be equalized.
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Old 01-01-2008, 12:53 PM   #9
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To answer your question, if the measured voltage at the battery immediately after the charger is inop is 12.5, the batteries are BAD. If that is the reading when the Inverter is running, you are probably ok.

A properly charged battery should read 12.6 min. after having a small load, overhead light not the inverter, for 10-30 minutes. (I am assuming your voltmeter is accurate to +/- .12 volts (1%)).
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Old 01-01-2008, 05:22 PM   #10
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I think 13.2 is as high as the battery should show. Perhaps your charger is a bit off. When you start inverting and show 12.4-12.5, that is not bad. A small load. Does you monitor show amp usage? How full are your batteries after you add distilled water? Just a tad below the ring or just a tad above the plates? Do you have a Link 1000 monitor? GaryKD asked a good question: How long do your batteries last before dropping to 12.0 and what are you using, lights, microwave, TV?
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Old 01-02-2008, 01:54 PM   #11
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<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Taking a voltage reading is not the best way to determine the condition of batteries. </div></BLOCKQUOTE>
the fact is that the voltage is a direct measure of the state of charge (SOC). Voltage and specific gravity both measure the charge status of a battery and both require care in making a proper and meaningful measure. With a modern DVM, voltage is much preferred as it provides results as good as those of hydrometry without the hazmat problems.

There is no such direct measure for the "condition" of the battery. This is usually measured by a load test or by conductance testing.

As noted, battery state of charge needs to be measured on a resting battery (inactive for half hour or more) that has had its surface charge removed or dissipated.
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Old 01-03-2008, 08:58 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">I think 13.2 is as high as the battery should show. </div></BLOCKQUOTE>

Maybe on some systems, but that would be a problem on mine. My battery charge controller won't even start charging the chassis batteries until the house system reaches 13.3V. My Xantrex RS2500 inverter/chargers brings the batteries to 13.4-13.6 when fully charged.

Every RV I've ever owned (7 of them) charged to around 13.6V
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Old 01-03-2008, 09:12 AM   #13
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Gary,

That is the converter output voltage, but the laws of physics and chemistry limit the peak voltage of a lead-acid 12V battery to 12.6.
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Old 01-03-2008, 04:38 PM   #14
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I've found being able to perform load testing on batteries very helpful. We have some collector cars, regular cars, the motor coach, and a bunch of equipment with batteries. It is easy for us to justify the tester.

Testers come in old technology (resistance loading) and new technology (mysterious electronics). I went with the new technology since it gives a wider range of tests and greater accuracy.

Any place that sells batteries will have a tester. The "technician" may or may not know the correct way to use the tester. The manual is always useful.
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