Acceptable Battery Impedance Value - HF Tester

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What is the industry accepted guideline for determining an acceptable battery impedance value? I tested a battery yesterday - it was a three year old Honda OE 51R battery. The tester showed the charge to be 100% and the CCA was a bit above the 400 spec. Voltage was normal, and the testing was done about 1/2 hr after shutdown. The impedance value was 6.90 mohm, which seems a bit high - and is what's concerning me. Can anyone provide some guidance on this matter? Thanks
 

JHZR2

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Doubling of impedance or 20% capacity loss is typically the condemnation value. Keep in mind that losses are load voltage (open circuit voltage - current*impedance), and that heat generation is impedance*current^2. Keep in mind that impedance varies with both temperature and battery state of charge. Additionally, different size batteries have different impedance values. That's why, unless you're looking to do the math, or have traceable data, often folks use a load test, as it critiques the battery in understandable terms. The. Or relations inside of the impedance testers should also be indicative, even if they have an error due to the above mentioned variations.
 
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NE,Ohio
Originally Posted By: The Critic
What is the industry accepted guideline for determining an acceptable battery impedance value? I tested a battery yesterday - it was a three year old Honda OE 51R battery. The tester showed the charge to be 100% and the CCA was a bit above the 400 spec. Voltage was normal, and the testing was done about 1/2 hr after shutdown. The impedance value was 6.90 mohm, which seems a bit high - and is what's concerning me. Can anyone provide some guidance on this matter? Thanks
was this on bare clean battery terminals? if not repeat it on bare, freshly cleaned terminals. Going through the battery clamps can add a significant amount of resistance. My 2011 forester's marginal oem battery was 8.xx I ended up replacing it as 300CCA was bad for -10F starts last year. I have a really crusty bad exide in my JD212 tractor.. it reads 12.xx it will be replaced this winter when the tractor is apart for maintenance.
 
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CT8

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15,392
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Idaho
Pretty much if the battery passes a load test it should be good. Keep it simple. I am happy for a 3 year battery life in harsh conditions. longer is mild conditions.
 

Win

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Arkansas
That sounds really high to me, as well, but it's hard to draw any conclusion without knowing how it has changed over time. The group 47 ever start Maxx I just put in my wife's car was 3.31 megohm at full charge, as an FYI. The battery I took out was at 5.49 megohm, and I kept it instead of turning it in as a core.
 
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562
Location
Sk, Canada
Originally Posted By: JHZR2
Doubling of impedance or 20% capacity loss is typically the condemnation value. Keep in mind that losses are load voltage (open circuit voltage - current*impedance), and that heat generation is impedance*current^2. Keep in mind that impedance varies with both temperature and battery state of charge. Additionally, different size batteries have different impedance values. That's why, unless you're looking to do the math, or have traceable data, often folks use a load test, as it critiques the battery in understandable terms. The. Or relations inside of the impedance testers should also be indicative, even if they have an error due to the above mentioned variations.
20% capacity loss, HAH! No way, try over 50% loss, or more. impedance does not grow in relation to capacity loss. I have an 8 year old Optima Red Top (when they were still made in USA) that still cranks very hard (Civic) but has about ~50% capacity now. Brand new it had an impedance of 2.5 mOhm, IIRC.
 
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