Quote:
Originally Posted by RCSP
Here is the battery I have now (see pic). I just checked and it's 12.9 volts. How can I test the battery to see if it is good?
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If you have a battery charger that you can control the charge rate, and it will put out at least 40 amp, there is an old test that gives a good idea if you have a sulfated battery or not. It's called the 3 minute sulfation test and was used for years in repair shops (before computerized testers).
Connect the battery charger and set it at a 40 amp charge rate and check voltage over a 3 minute period. If the voltage rises over 15.5 volts during that 3 minute period it's an indication that the battery is sulfated and may never take a full charge again.
This test is best done after the battery has been discharged enough to take away any "surface charge". If you don't have a load tester, and the battery is attached to a vehicle/trailer, just turn on lights, fans, etc for 10 minutes or so. Then run the test.
Of course another test is to just turn on all the various loads in the trailer and see how long the battery stays above the fully discharged voltage for whatever temperature is that day. The battery in the picture should last just over 3 hours with a load of 25 amp when brand new. Whatever time you get could just be used to determine a percentage of battery "life" you have remaining.
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