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Old 10-09-2012, 10:27 PM   #1
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Battery voltages

Am a little embarrassed to ask this question because I know it's on this forum somewhere but, I can't find it.

I finally bought a digital volt meter and would like to check the health of my batteries.

What should a full charge read?
How about the low voltage where the batteries should be recharged to prevent damage?

Thanks

Bill
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Old 10-09-2012, 10:49 PM   #2
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At least better than 12.6 volts. The closer to 13, the better.
That said, a voltage reading is not a true read on how good a battery really is. There are better diagnostic checks for how good a batter really is.
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Old 10-09-2012, 10:54 PM   #3
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Quote:
Originally Posted by bend302 View Post
Am a little embarrassed to ask this question because I know it's on this forum somewhere but, I can't find it.

I finally bought a digital volt meter and would like to check the health of my batteries.

What should a full charge read?
How about the low voltage where the batteries should be recharged to prevent damage?

Thanks

Bill
it should read 12 volts on full charge and battery charger is not on. you should start charging at 11 volts because most elec, 12 volt componats are at risk of damage below 12. it realy all about the Amper Hours that the batterie is rated for. It would take me to long to explain because i am a one finger typer. but google 12 volt batteries for the complete story
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Old 10-09-2012, 11:06 PM   #4
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Took this: "All Lead-Acid batteries supply about 2.14 volts per cell (12.6 to 12.8 for a 12 volt battery) when fully charged. " from a really good website on 12v batteries and wind and solar power:

Deep Cycle Battery FAQ

Lots of great info here. What you are looking for is well down the page.
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Old 10-09-2012, 11:21 PM   #5
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Here are the voltage to capacity charts.
I printed them out and keep them right in the battery compartment.

The first chart is the "idiot light" voltages.

NOTE: The idiot lights do NOT read "full" and "empty"; they are "C" (charging) and "L" (low). "G" (good) is lit as long as the voltage is above 1/2 capacity.
When it goes out, you should hook up your generator.
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Old 10-10-2012, 12:54 AM   #6
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Awesome Herk. Thanks! Just saved them both to my iPad.
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Old 10-10-2012, 07:42 AM   #7
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Quote:
Originally Posted by johnemt View Post
it should read 12 volts on full charge and battery charger is not on. you should start charging at 11 volts because most elec, 12 volt componats are at risk of damage below 12.
Hi John, 12v = full charge is a common misconception. As you can see
from the chart Lou posted- 12 V is around 50% charged. This means
when you reach 12v it's time to re-charge because for longest battery life
you don't want to discharge below 50% if you can help it.

Having said that I have been known to drop below that point a time or
two when we're boondocking.
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Old 10-10-2012, 07:51 AM   #8
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If you're planning on boondocking, a really good reference is "Managing 12 Volts: How to Upgrade, Operate, and Troubleshoot 12 Volt Electrical Systems". I found that on another post - it is worth the price and then some.

Remember, checking the battery as it is being charged won't tell you the battery output, just that of the charger. After it has been removed from charge, the battery carries a fake voltage level because the electrolitic has a higher charge close to the cells. Wait about 24 hours after removing from charge before checking voltage output.

A hydrometer is a better test of battery health. It lets you know how healthy the chemical reaction in. That is where the specific gravity on Herk's chart is REALLY useful.

One thing I have not seen very mentioned very often is that as these batteries charge and are off-gassing, they are losing water, so check the fluid level. Car batteries don't need that anymore, but these deep cycle batteries do. I found that I was about a quart low after 2 months recently. Top off the cells with distilled water (spring water, well water, and city water can contain plate damaging impurities) and get a good charge on it before testing.

That said, a volt-meter is really handy for other uses like checking the health of the AC power coming in at the campsite.
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Old 10-10-2012, 08:13 AM   #9
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IMO, if you are losing water "at all" you have a problem. Today's 3 stage chargers moderate the charge rate to nearly eliminate water loss.

My camper is hooked up 24/7 to my house and the batteries stay connected to maintain their charge. I have "topped off" twice (less 1/4 cup in total and spilled most of it out of the battery bulb) in 3 and a half years.

Look for a cracked case or a failed third stage in your converter.
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Old 10-10-2012, 08:40 AM   #10
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It did not seem odd to me relative to other deep cycle applications I've used, but I will have to check the charger now.
I suspect the black battery box and some direct sun exposure helps the evaporation. The water was evenly low in each cell, so the case is OK; no sign of loss in the container.
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