Modern Car Battery Testers w\LCD - Accurate?

[killingtime]

Hi,

I was looking to buy a 12v car battery tester and noticed there's a new breed of cheap tester with LCD displays (<$20) doing the rounds. They've been around a few years now.

The old style testers have a large low resistance heating element and draw around 100A. An analogue meter then tells you the voltage under load and you work out from that if the battery is any good based on the meter markings. Like the models attached. The small one is a fixed 100A and the larger blue one is variable up to 500A.

The new style testers have a LCD and only pull a small current (~1A), then tell you if the battery is any good. You input the CCA rating of the battery before the test and the display tells you the actual CCA rating of the battery, even though it didn't draw that current. Interestingly, the CCA value you enter doesn't change the draw current for the test. There's a technical review & strip down of the Kingbolen BM550 on yt at the link below and it uses a 11 Ohm fixed resistor to load the battery.



Another review here with the same tester on good and bad batteries at different SoC and it's clear you need to fully charge the battery before the test if you want accurate readings. The 'State of Health' (not State of Charge) reading seems to vary a lot based on how well charged the battery is.



I'm guessing that the meter works out the internal resistance of the battery using the load/no load voltage difference at a known current (~1A) and then uses this value to work out what the battery might be capable of under actual load using a look up table.
If you knew what the look up table was you wouldn't need the tester. You could just load the battery down with cheap resistor and take before & after voltage readings with a DMM. Wouldn't be as convenient though.

Do you think these new testers are as good as the old full current ones?

Thanks.

[edpalmer42]

I have a similar unit.  I wouldn't trust its accuracy, but I think it's useful to indicate whether the battery is starting to age.  Over time, the internal resistance readings will rise and the SOH readings will fall.

There are no standard definitions for 'good', 'marginal', and 'bad' so you have to decide what results make sense for your application.  For example, my Prius Prime only uses the 12V battery to boot up the computers, run a few lights, fans, pumps, etc.  So if the tester says that my battery is bad because it will only provide 50A of current, that's fine because I know that the battery drain during starting is only 25A - 30A.  Of course, since my battery is rated for 295A CCA, a 50A result would mean that I should be looking for a new battery!

Ed

[Shonky]

As above. I have a Topdon one and it seems relatively ok. Had a battery recently that was definitely on the way out. A Ctek charger didn't like it either. Tester reported appropriately bad result. Brand new replacement battery then reported an appropriately close to full SOH.

So yeah a good indication of state of health but not as good as a carbon pile tester or similar.

Another option that is somewhat useful for testing a battery is a BM2 bluetooth or similar battery monitor. Ignoring the potential privacy issues of the APK (see thread in this forum), the cranking voltage sag test I find is a pretty good indicator (if the battery is charged before cranking).

[killingtime]

Thanks for the replies. I'll get an electronic one then.

I was going to buy a 100A one and after looking around I noticed that all the banded 100A testers (Sealey / Draper etc) only went to 500 CCA on the scale, but the China ones (identical design) went to 1000 CCA. Higher is better obviously as it means being able test a greater range of batteries. The scale caught my eye though. See attached.

The green section of the scale on the right with the CCA markings on it is stepped. It marks the point at which a battery is Good or Weak while under load on the tester. I got the Sealey BT91/7 scale from their instruction manual. The China copy scale came from Ali and they're all the same. Both units pull the same current ~100A.

The CCA scale on the China copy sits in exactly the same place on the voltage scale as the Sealer unit, even though the CCA ratings are different, so they both can't be right as they both pull the same current. On the Sealey unit, 11.2v is the limit for a 500 CCA battery, but on the China unit 500 CCA equates to around 10.4V & 11.2v is the limit for a 1000 CCA battery.

Given both units pull the same current it looks as though they've just changed the CCA numbers on the scale but kept everything else the same including the stepped part between Good and Weak . The giveaway comes from the instructions on the back of the copy unit for temperature adjustment. The instructions talk of 50 CCA steps for differing temperature bands - which is correct for the Sealey \ Draper originals, but wrong for the copies as they're stepped at 200 CCA.

If I'm correct then anyone buying these copies has a scale that's wrong and weak batteries could show up as good. 

[edpalmer42]

Don't overthink this.

None of these devices are lab-quality.  They're all kinda-sorta-maybe-probably devices.  They will all give you numbers that don't agree with any other device or with any recognized standards.  After all, how can you measure Cold Cranking Amps at room temperature??  They're all using fudge factors and voodoo math to approximate the results.

But they will all give you useful info on the state of your battery.  You may end up using two different styles of meter to measure different battery characteristics.

But regardless of what meter(s) you use, always use the device between your ears to decide whether the results indicate good, okay, or time to go shopping!

Ed

[Benta]

A good multimeter will do the same and be useful in many other areas as well. Save your money.

[Peabody]

It seems to me that none of these meters are very reliable in absolute terms.  If you take a single reading, the result may be misleading.  But if you take readings periodically over time, a change in the reading should really indicate a change in the battery's state of health.  That's assuming you always test with the battery fully charged, and when the temperature isn't at an extreme.

I opted for the 100A "toaster" meter.  And I use a battery "minder" overnight ahead of testing that trickle charges the battery.  The keys are the voltage the battery drops to under load, and whether it holds that voltage or continues to drop.

But if a battery makes it to six years (much less for Honda/Acura vehicles) I would be pretty much ready to replace it at the first sign of deterioration.  It's not going to last much longer in any case, and I want to change it out at a time of my choosing.

[killingtime]

After doing some more research, I stumbled on the article below about different battery test methods.

I was surprised to learn that the DC load test and AC conductance test yield very different internal resistance results for the same battery and both results are correct, they're just testing the same battery under different conditions.

Quote:

The 1,000-hertz (Hz) ohm test is another common method. A 1,000Hz signal excites the battery and Ohm’s law calculates the resistance. Note that the AC method shows different values to the DC method when measuring a reactive resistance, and both readings are correct.
For example, Li-ion in an 18650 cell produces about 36mOhm with a 1,000Hz AC signal and roughly 110mOhm with a DC
load. Since both readings are valid, yet far apart, the user must consider the application. The pulse DC load method
provides valuable readings for a DC application such as a heating element or an incandescent light, while the 1,000Hz
method better reflects the performance requirements of a digital load, such as portable computing and mobile phones that rely to a large extent on the capacitive characteristics of a battery.

So, when you test a battery with a dedicated meter, it's necessary to understand how the meter tests the battery, and you also have to know how the battery will be used so you pick the correct test method.

In my case, the DC load test would be more appropriate for a battery that's starting an engine. It would yield a resistance value that's more likely to be seen by the starter motor than the AC test.

I'll bet every manufacturer out there uses a test method that yields the lowest internal resistance result so they can print that in their literature. Without knowing the method they used, the AC frequency, the temperature, SoC etc, the spec sheet information is meaningless. You might never see that IR in your usage scenario.

Someone posted a question on SLA IR back in 2022 below. His IR measurements were about 20x higher than the Mfrs and he couldn't figure out why. I'll bet the above had something to do with it.

https://www.eevblog.com/forum/beginners/measuring-the-internal-resistance-of-a-sla-12v9ah-battery-help!/

[thm_w]

Some discussion here about AC ESR: https://www.eevblog.com/forum/renewable-energy/battery-impedance-measurement-esr/

You shouldn't compare DC to 1kHz AC reading, or a 80% charged reading to a 40% charged reading yeah. But, the reading does generally seem to scale up, probably good enough for us hobbyists, to just choose the ESR method and use that for our evaluation.

Spec sheet should be DC unless specifically stated otherwise.

https://www.mdpi.com/1996-1073/11/1/118
https://www.researchgate.net/figure/Typical-impedance-spectrum-of-a-battery-in-a-frequency-range-from-millihertz-to_fig1_320662558

[Wrenches of Death]

But if a battery makes it to six years (much less for Honda/Acura vehicles) I would be pretty much ready to replace it at the first sign of deterioration.  It's not going to last much longer in any case, and I want to change it out at a time of my choosing.

My "limit" is four years for both of the cars and the pickup, even with it's dual batteries. It's not worth the worry or hassle of the wife or I getting stuck some where.

I have a traditional automotive carbon pile type battery tester that I will usually test them with. Other than a couple of crib deaths over the decades, I've had pretty decent luck with batteries.

My only exception to the four year rule is for the tractor. I'll repace it the first time I notice a decrease in cranking speed, especially after using the glowplugs. Low voltage and slow cranking speeds is death to diesel starters. Five to seven years is typical. Since I can buy five or six batteries for the price of a starter, when in doubt......

WoD



 

[Swake]

Those small cheap electronic meters are reliable and precise enough that you can trust them. It is not possible to perform the same measurements with a multimeter alone.

The rules I apply for long lasting lead-acid batteries:
1/ Start with quality batteries, not the most expensive, and certainly not the cheapest. Actually the best thing you can do is to compare the weight (for same size) as it is a direct indicator of the thickness of the lead plates which is the 'wear' element.
2/ Never, NEVER !!, deplete more than 50%. After a big discharge always, ALWAYS!!, recharge within the next 24 hours, preferably with an slow electronic charger. 1 Ampere for a bike/quad battery, 5 A for a car battery, 10 A for a bigger traction battery). Ambient temperature. AGM/Gel batteries need a somewhat higher voltage. Don't use the big old heavy chargers, these are generally unregulated and not adapted to the batteries of the modern world.
3/ Winter storage: Do not use a trickle-charger or winter-charger continuously. Disconnect the battery unless you trust the vehicle will go to sleep mode and consume virtually nothing, then charge the battery to 100% with a slow electronic charger. Top-up the battery every couple of weeks (configure a reminder in the calendar of your phone).