How to interpret these test results?

[Carmudgeon]

I recently picked up one of those electronic battery testers on sale, keeping in mind that don't perform load testing (which is really the only/best way to determine the state of a battery), but still having some faith that they can at least produce a somewhat reasonable assessment.

After using it, I'm not so sure, or how to interpret the results, other than to perhaps rationalize that they function within a narrower scope than I expected:

These results are from a roughly 8.5+ year old battery (70Ah H6), or one than has been in service for 102 months.

In practical use, it will just barely crank over the car if it hasn't been driven for a few days, even after being given a full charge, from both a smart charger (CTEK), and an old school dumb charger (Schumacher).

I know it's not a "good" battery, and due to be replaced, but according to the tester, it is in much better condition than I have observed.

Granted, this thing was cheap, and not a professional grade tool, nor part of an exact science, and relies on a lot of assumptions, but how much faith can I really put into it?

 

[dishdude]

Time to go battery shopping. Have to add up everything around, if this was sitting on the shelf or in a car that hadn't run for a month you might get away with charging it and retesting, but if this is from a vehicle with a good charging system or just off a charger it's time to replace.

 

[Rand]

Its almost dead- needs charged up, and possibly ok for another year or 2 depending on application.

I would charge it full, retest,.. and do a load test.

IF you dont have a carbon pile tester, you can do a load test with a Meter while starting the car.

 

[Carmudgeon]

Its almost dead- needs charged up, and possibly ok for another year or 2 depending on application.

I would charge it full, retest,.. and do a load test.

IF you dont have a carbon pile tester, you can do a load test with a Meter while starting the car.

I've actually been stringing this battery along, knowing that it won't hold a charge, but can be kept "alive" with a charger, and under certain usage patterns.

It's not in a daily driver, or the sole means of transportation, so I've been procrastinating in getting it replaced.

I know the battery is nearly kaput (and the charging system is good), and that's what I was expecting the tester to tell me, but if it thinks the battery is "good," how can I trust such a tool, or why should I want to keep it, even if it was cheap? That's the real question.

This is probably as easy of a test case as it can encounter, and has seemingly failed.

 

[Rand]

Capacitive testers arent miracles..
IMO they are more accurate when the battery is fully charged.
but best used with common sense and other tests if appropriate.

Trust but verify

 

[bullwinkle]

12.07 VDC isn’t even close to fully charged for lead-acid (should be 12.6), and an AGM should be 12.85-battery isn’t fully charged, and a parasitic draw may also be pulling it down. Now, if you charge it with a smart charger (preferably one that can handle AGM), and it still cranks slow at 12.85, then I agree it’s shot.

 

[shortyb]

Sounds like you took all factors in totality and interpreted the results well. The battery is on the way out. Your instincts confirmed what the "tester" could not with any form of assuredness. Sounds like the tester gets relegated way down the list when it comes to what you use to determine when your batteries go. Did you keep the receipt?

 

[Craig in Canada]

I'm no PhD chemist but your post has me wondering if you don't actually have some kind of parasitic draw in the car. Generally I experience/read about battery end of life characteristics that are one of:

• reduced CCA - inability to deliver enough current to start the car, especially as temperature drops
• individual cell short - terminal voltage 10.8V (usually happens suddenly one start)
• reduced Ah - stores less energy and goes dead more easily

None of those is "goes dead by itself if you let it sit for 2 days". It's true, you may have such dramatically reduced capacity/Ah but, doing the math: It's said "out there" that standby sleeping currents shouldn't be any higher than 50mA (true? Don't know) and I know my vehicles are less than half that.

0.05 A * 48h = 2.4 Ah.

The 12.07V you show in your pic is around 30% charge for standard lead acid (not factoring in temperature so it's just approximate) so that 2.4Ah would be ~70% of the battery's capacity.

So your battery capacity would have to have fallen to <4 Ah for a vehicle with typical max standby current to make it unstartable in 2 days.

Does that make sense? Even if my math is off here and there, it's just an illustration. Fudge everything and call it 10Ah. I'm not so sure that you'd have a battery so bad that it dropped capacity from 70Ah to 10Ah, but the tester still shows good CCA and internal resistance. Sure the battery is old enough that it doesn't owe you anything, but you may still have another problem if you don't look for it, and you'll still have issues after you buy a new one. You might buy a new battery and then make it to 3 or 3.5 days parked before it barely starts.

 

[SR5]

That voltage seems low for a resting battery, I would expect 12.6 to 12.8 volts.

When it's connected to the car and running, you would expect 13.5 to 14.5 volts.

When starting (cranking) the car you would expect 10 volts or higher.

A resting battery that you have recently charged up, showing only 12.07 volts after a few days looks like a dud to me.

 

[SubLGT]

..........Granted, this thing was cheap, and not a professional grade tool, nor part of an exact science, and relies on a lot of assumptions, but how much faith can I really put into it?

I also have a cheap digital tester, that I only use for testing internal resistance. I don't trust it for testing CCA or battery health. I do 100% trust my carbon pile tester.

 

[Carmudgeon]

Interesting responses. In hindsight, perhaps I should have chosen a different way to phrase the question -- "Would you trust these test results, given the facts?" and probably received different answers. My old marketing research prof would probably wag his finger and remind of the effect of how questions are posed affect the results, and should be carefully considered.

Anyway, I am aware that the SoC was at a low state, and not freshly recharged. However, the tester predicates accounting for only two conditions -- in car, and outside of car -- not SoC state, and does not specify that a battery must be recharged, or at full charge to perform testing. The "Good -- Recharge" indicator also tacitly acknowledges that there are no assumptions or preconditions, aside from in/out of car. But, I will put it on a charger, and see if it affects the results.

I've also owned this car long enough, and replaced enough batteries in it to know that it's behaving as expected for a weak battery at the end of its life cycle. The charging system is good, and if/when a replacement is installed, there should be no anomalous behavior to suggest there is an abnormal resting drain.

The best analogy off the top of my head is if an instant OLM sampling test returned "good" results on a sample of oil at the end of a 2-year, 15,000 mile OCI.

One would not trust that the OLM, which can only base its results on the specific characteristics it measures, and make assumptions from there, over the practical knowledge that 2-year old oil that has been run for that duration is that close to being considered "good" or closer to being fresh than spent.

With that knowledge, most would question the integrity, or faithfulness of the tester, as in this case.

I did going into it knowing that it would have constraints on its accuracy. I just didn't know that they were this low, or low enough to cast such doubt, or question its actual utility.

 

[macarose]

Interesting responses. In hindsight, perhaps I should have chosen a different way to phrase the question -- "Would you trust these test results, given the facts?" and probably received different answers. My old marketing research prof would probably wag his finger and remind of the effect of how questions are posed affect the results, and should be carefully considered.

Anyway, I am aware that the SoC was at a low state, and not freshly recharged. However, the tester predicates accounting for only two conditions -- in car, and outside of car -- not SoC state, and does not specify that a battery must be recharged, or at full charge to perform testing. The "Good -- Recharge" indicator also tacitly acknowledges that there are no assumptions or preconditions, aside from in/out of car. But, I will put it on a charger, and see if it affects the results.

I've also owned this car long enough, and replaced enough batteries in it to know that it's behaving as expected for a weak battery at the end of its life cycle. The charging system is good, and if/when a replacement is installed, there should be no anomalous behavior to suggest there is an abnormal resting drain.

The best analogy off the top of my head is if an instant OLM sampling test returned "good" results on a sample of oil at the end of a 2-year, 15,000 mile OCI.

One would not trust that the OLM, which can only base its results on the specific characteristics it measures, and make assumptions from there, over the practical knowledge that 2-year old oil that has been run for that duration is that close to being considered "good" or closer to being fresh than spent.

With that knowledge, most would question the integrity, or faithfulness of the tester, as in this case.

I did going into it knowing that it would have constraints on its accuracy. I just didn't know that they were this low, or low enough to cast such doubt, or question its actual utility

Just an FYI... Love you getting the most out of your battery but just in case you decide to move on here's what helps me with these types of garage queens.

Advance Auto Parts often has 'seconds' that they call used batteries in their back shelf. They are only around $40. You won't see them in the retail space but if you ask to use the bathroom, just look for where a bunch of batteries are getting charged.

Next to that will be a bunch of batteries with yellow stickers.

Just go buy the largest one that will fit in your battery space for that vehicle. Enjoy another 8+ years of freedom.

 

[Carmudgeon]

Just an FYI... Love you getting the most out of your battery but just in case you decide to move on here's what helps me with these types of garage queens.

Advance Auto Parts often has 'seconds' that they call used batteries in their back shelf. They are only around $40. You won't see them in the retail space but if you ask to use the bathroom, just look for where a bunch of batteries are getting charged.

Next to that will be a bunch of batteries with yellow stickers.

Just go buy the largest one that will fit in your battery space for that vehicle. Enjoy another 8+ years of freedom.

Yeah, I've seen those before, as well as the blems that Interstate sometimes sells. I have no problem ordering a new battery and will do that shortly.

For the sake of curiosity/completeness, I did put the battery on a dumb charger for about 5-6hrs in auto mode, which left it at 12.6v, close to full charge, or at full charge for such an old battery, removed the surface charge, then retested:

Input type = 70 Ah capacity

Input type = 720 CCA

These types of tester have their limits, which it turns out has been discussed here before, and might be able to reveal some parameters that could be of use for consideration, but as far as the conclusions, particularly health and overall condition, the figures it provide speak for themselves.

Midtronics has this to say about the subject:

Good battery, recharge​

It’s also possible that a battery test returns as “good – recharge” when the battery is either good or it fails. If the test is performed with incorrect vehicle information at a higher CCA than the actual battery, this result could be indicated for a perfectly healthy battery.

But a bad battery can also return the result of “good – recharge” if it’s sulfated. It’s sometimes the case if a battery has been stored without a full charge and the sulfation becomes permanent. It might not be possible to restore the battery to full capacity. A good-quality tester can identify the condition while a non-specialized piece of equipment like a common DVOM might not.

Bottom line -- know your tool, and its limitations, and don't blindly trust it, as it appears many do.