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Old 06-22-2018, 10:57 PM   #1
Snowdrift
 
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Default Testing and charging rv batteries

My 2012 great western van has 4 - 6 volt batteries. I am going on a long trip to Alaska and I want to test these batteries to make sure they are still holding a total charge. They still are working but since they are six years old I want to be sure I won’t have problems with them on my trip. I took one of them out and took it to an auto store but they only test 12 volt batteries. Does anyone have any suggestions?
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Old 06-22-2018, 11:16 PM   #2
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Default Re: Testing and charging rv batteries

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Originally Posted by Snowdrift View Post
My 2012 great western van has 4 - 6 volt batteries.
I assume the bank is in a series-parallel configuration and delivers 12 volts? One simple/quick test is to fully charge the batteries and then apply a load and verify amp-hour capacity, i.e. if you have a 400 ah bank apply a 20-amp load and check after 10 hours at which point you should be at 50% capacity and voltage should be about 12.0 under load or 12.2 no load. This test requires only a voltmeter and ammeter.

The above check is crude but should indicate if the batteries are in reasonable shape. There are more thorough tests to be sure but they would require more test equipment or a battery management system.
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Old 06-23-2018, 12:24 AM   #3
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Default Re: Testing and charging rv batteries

The old-fashioned way is to charge the batteries, then measure the specific gravity of *each cell's* electrolyte with a hydrometer.

Adequate hydrometers are pretty cheap (or ask a battery shop to test them).

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Old 06-23-2018, 12:32 AM   #4
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Default Re: Testing and charging rv batteries

Specific gravity indicates state of charge but does not necessarily test battery capacity.
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Old 06-23-2018, 12:41 AM   #5
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Default Re: Testing and charging rv batteries

Quote:
Originally Posted by Snowdrift View Post
... I am going on a long trip to Alaska and I want to test these batteries to make sure they are still holding a total charge. ... Does anyone have any suggestions?
I'm normally a use it 'til you can't no more type of guy.

In this case...
If original, your battery bank is 6 years old. Has the bank ever been discharged to below 50% SOC? That reduces service life. Do you plan on dry camping often or using campgrounds?

Factors to me are reliability, peace of mind, and cost. You may avoid replacing batteries for some time, but they won't last forever. What is the cost of a bank of batteries when compared to the overall costs of the trip?

We did a really great trip out west last October. I had some ideas of expected cost, but I admit that I didn't do a detailed project estimate. When I totaled the fuel costs it was a bit of a surprise. Using the total miles traveled and an average mpg number showed that the actual fuel cost should have been expected, but I digress.

If the battery condition tests great, go for it. If at all in question the bank should probably be renewed.

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Old 06-23-2018, 12:50 AM   #6
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Default Re: Testing and charging rv batteries

You can use your inverter and a mechanical fool-the-burglar timer. Set the timer to midnight, plug in 4 old fashioned 60W filament type bulbs for a 20 amp load. One deep discharge isn't going to seriously cut down your cycle life. Let it run down till the inverter hits its cutoff voltage (at which time the timer will stop advancing.) Read the timer - should be 20ish hours later. Completely recharge the batteries promptly.

The timer in this case is functioning only as a clock that won't forget when the inverter power cuts out - so you don't have to stay around and baby sit the test.

Last edited by rollerbearing; 06-23-2018 at 12:57 AM.
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Old 06-23-2018, 12:55 AM   #7
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Default Re: Testing and charging rv batteries

Again, one deep discharge isn't going to kill the batteries. It will provide a full picture of information and may actually save you from retiring a bank that may still have a good amount of life left in it. The key though is to recharge completely and promptly!
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Old 06-23-2018, 01:29 PM   #8
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Default Re: Testing and charging rv batteries

Thanks for all your great ideas! We will let you know how things work out!
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