Battery load test numbers

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An easy test is to apply a load of 1/20th of what the batteries are rated for and seeing how many hours it will run until the voltage reaches 10.5V. So if your GC2's are 220Ah you'd apply an 11A load and start the clock. A new/good battery will go 20 plus hours. 15 hours would be 75%, 10 hours 50%, etc. This way you get a hard number of merit based on the same way battery capacity is specified.

Mark B.
Albuquerque, NM
 
I removed all 4 batteries for an inspection,, the two rears in the container are hidden by the front two and a bitch to get to,, by removing them I found massive corrosion that was the root cause of my problem.. The batteries are only 3 years of age and I normally get a solid 6 years out of them.. This last year has been very trying with maintenance on anything around the ranch do to fighting my wifes cancer all year and loosing to it.. Now am back on the road as of 5/2 24 and will place her remains in the ground on her 80th birthday ( the 8th.) in a small town in central North Dakota where she will lay with her mother,, father,, and my son>>>Dan
 
Good to see you found the problem and it wasn't the batteries themselves.

I want to answer your original "good number" question because it's a good one and of general interest. Most battery load test devices are designed to measure voltage under some level of load and for a given CCA rating. A typical tester calls for applying a load equal to 50% of the battery CCA rating for 15 seconds and then measuring voltage. An acceptable result for a 12v lead-acid battery is about 9.6v @ 70 F. A few tenths less if cooler. A higher number is even better. Some testers just show a Poor-Fair-Good scale rather than actual voltage numbers. Always follow the instructions for the actual tester in use.

It's a valid criticism that a CCA load test is not a good measure for deep cycles. However, it's still a useful test. If a deep cycle fails the CCA test, you can still safely conclude the battery needs to be replaced. The shortcoming is that a deep cycle that passes the test with a voltage that is only marginal, you cannot be sure the battery is "good". The reason is that deep cycle loads are usually lower than a 50% CCA but last much longer. A battery that can manage a 15 second load can still die rather soon when given a moderate but long-lasting amp load.

If your battery only states an Amp-Hour (AH) rating but your tester is calibrated for CCA, multiply the AH by 7.25 to get an approximate CCA. It's not a 100% accurate conversion algorithm, but close enough for this type of test. Thus a 100 AH deep cycle can be tested as if it were an 725 CCA battery.
 
All well and good,, I have a load tester but not up the anticipated load of this bank,, so I had intended to take them to my local NAPA store for testing,,, that is until I discovered the likely problem..Thanks again>>>Dan
 
Utclmjmpr said:
that is until I discovered the likely problem..
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Let us know the result as you clean up and resolve the problem that you found. And also, my condolences to you for the loss of your wife. I have been married now for 61 years and mine is not in the best of health so that loss does cross my mind at times.
 
I think my load tester says .. Well let me look
it says: (And I copy from manual)
Turn the Load Knob (C) clockwise until theDC ammeter reads 1/2 the Cold Crank Amp(CCA) rating or three times the amp-hour

this is a 15 second test. when it beeps read the voltage dial and disconnect
WEAR GLOVES.
 
Kirk,,, We were married 61 years 7 days..The problem for me know is not her death,, what is bothersome now is the way the surgeons butchered her up ( twice ) prior to death,,AND the hospital plus surgeons were paid $ 565,600.00 for the job..>>>D
 
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Utclmjmpr said:
All well and good,, I have a load tester but not up the anticipated load of this bank,, so I had intended to take them to my local NAPA store for testing,,, that is until I discovered the likely problem..Thanks again>>>Dan
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A load tester is for testing only one battery at a time, unless you have a huge tester with the capacity of half the total bank AH, and that would not ID one bad battery..
 
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John From Detroit said:
Be aware there are different testers and some will show 'Bad' on a battery that is still got years left in RV-HOUSE or good on one that's bad.
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Speaking of load-testing; the battery in my Silverado PU is dead after 5 days of not being started. Took it to Interstate last Nov. they tested it and declared it good. Took it back in Feb., they tested it as declared it good. It still goes dead after 4 days now. Interstate told me I had a big phantom draw, I bought a DC clamp-on ammeter and tested the draw, 0.32A. Is that enough to drain the T8 battery in 4 days?
 
.32 amps times 24 hours times 4 days is about 31Ah. That's a bit light for a battery that should be around 90Ah. But it could be it's not starting out at 100% either, or you happened to measure .32A and at other times the load increases. But for sure .32A is a lot higher than typical "off" vehicle battery draw so it's something to chase down.

Mark B.
Albuquerque, NM
 
Mark_K5LXP said:
.32 amps times 24 hours times 4 days is about 31Ah. That's a bit light for a battery that should be around 90Ah. But it could be it's not starting out at 100% either, or you happened to measure .32A and at other times the load increases. But for sure .32A is a lot higher than typical "off" vehicle battery draw so it's something to chase down.

Mark B.
Albuquerque, NM
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Mark, I measured that on the accessories/computer supply cable which has a 150A blade fuse inline. Tomorrow I'll disconnect that cable from the positive post and measure the main starter cable.
 
Ray-IN said:
Speaking of load-testing; the battery in my Silverado PU is dead after 5 days of not being started. Took it to Interstate last Nov. they tested it and declared it good. Took it back in Feb., they tested it as declared it good. It still goes dead after 4 days now. Interstate told me I had a big phantom draw, I bought a DC clamp-on ammeter and tested the draw, 0.32A. Is that enough to drain the T8 battery in 4 days?
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Let's do the math. .32 amps times 96 hours rounds to 30 amp hours.
T8 battery (per Interstate) is 90 amp hours
Starting batteries need to be 80% or better so yes.
 
Now to locate and remedy the drain; have I mentioned I hate 12V problems. Humm, I wonder if the computer is using advanced AI?:sneaky:
I used my load tester 1 hr after recharging, and it shows barely into the OK/green range @ 200A.
 
I found the phantom draw, it was the Tekonsha Prodigy brake controller I installed a few weeks ago. Today I re-read the installation instructions and user manual. This particular brake controller never shuts off, instead it goes to "sleep" when unused.
The solution is to unplug the connector on the back of the unit until it's needed again.
 
Ray-IN said:
The solution is to unplug the connector on the back of the unit until it's needed again.
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I had the Prodigy also and like yours it was asleep when not in use but I often left my truck sit for more than a month between uses during the winter months and never had any problems. With a diesel truck I did have two group 94 batteries in parallel. My son was also running a Prodigy in his Toyota gas truck that he towed with and had no problems.
 
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