Battery tester - Page 1
Forum section: electronics / beginners

author: BeBuLamar
author_rank: Super Contributor
timestamp: March 23, 2025, 11:52:11 am
content: I see a lot of battery testers for sale but I don't think you can trust them. So if you are going to build one for 1.5V cells what kind of load should be and what's the range of voltage for good? Also do you need different load for different battery size like a D vs AA?

author: Ian.M
author_rank: Super Contributor
timestamp: March 23, 2025, 12:33:04 pm
content: The appropriate load depends on the battery (cell) type, size and chemistry, and the voltage limits for 'good' depends on the cell chemistry, the application circuit, and the expected usage. Therefore there is no 'universal' simple battery tester circuit - a tester that's good for alkaline D cells will probably indicate all new Zinc Carbon AAA cells are bad!If you take the cells out of a gadget as soon as they run out, let them sit for a day and test them on a specific tester, you can determine a lower limit for *that* tester. A brand new cell of the same type gives you the upper limit. The 'good' threshold will be somewhere in between, depending on the behaviour of the gadget as the cells weaken and how important it is to have a lot of life left. e.g. in entertainment industries it is common practice to change microphone batteries every day without even testing them because the cost of even premium brand batteries is negligible compared to the costs if a shoot/session is interrupted by battery failure.

author: RoGeorge
author_rank: Super Contributor
timestamp: March 23, 2025, 12:48:29 pm
content: Tried many versions, including the kind that can tell mAh and such. Believe it or not, this is the one I use the most:https://www.eevblog.com/forum/chat/invention-of-the-day-the-battery-tester-with-zif-socket/Can tell you in 2 seconds if a battery is discharged or not. Works for recheargeable, too.

author: Ian.M
author_rank: Super Contributor
timestamp: March 23, 2025, 12:53:41 pm
content: I favour the cheap LCD bargraph type for making quick keep/recycle decisions on used batteries. Some gadgets squeeze every last bit of 'juice' out of their cells, and any that come out of them go straight to recycle.However RoGeorge's suggestion is probably the appropriate amount of time and effort for building one, as anything more complex is probably not going to give a worthwhile return on time, effort and parts cost vs simply fitting decent quality (i.e. *NOT* Durahell) brand new in-date Alkaline cells when the previous set run out, and keeping a spare set handy.

author: GLouie
author_rank: Regular Contributor
timestamp: March 23, 2025, 03:42:33 pm
content: I think it's a bit of a fool's errand to get "accuracy" from a battery tester, and I do like RoGeorge's solution!One popular tester from ZTS (I have one) apparently uses a different load for different battery types/voltages, and has a prorietary look-up table they compare the voltage to, displaying a % on a segmented LED bargraph. There's a patent.As noted, it's rough since it's only one load and many groups are broad, such as all 1.5v alkalines using the same terminal. But, it give a reassuring grade for people who want that. ZTS testers are not cheap, and a cheap tester is probably for most practical purposes just as useful.

author: PlainName
author_rank: Super Contributor
timestamp: March 23, 2025, 03:53:41 pm
content: QuoteJust had a coin cell that was reading 3.1V on the meter and battery tester, and seemed to be fine, but the garage opener it was in wouldn't work. I'd passed it off as the opener being faulty (cheap from Ebay...) some time ago, but uncovering it again I checked the voltage as it was working, and it dropped to 2.4V. A real PSU in current monitoring mode showed no excessive load, and changing the battery for a new one fixed the issue. I wish my simple battery tester had used a real load to test instead of just checking no-load voltage.

author: Ian.M
author_rank: Super Contributor
timestamp: March 23, 2025, 04:06:57 pm
content: Find the typical load resistance the battery manufacturer specifies for life tests, (in the datasheet or if not known, use the datasheet for a similar battery of the same size and chemistry that does give a load resistance), take two clip leads, and connect the resistor across your DMM probes. For anything larger than a coin cell, its probably going to need a power resistor. You now have a cell-size appropriate battery tester.

author: bdunham7
author_rank: Super Contributor
timestamp: March 23, 2025, 04:40:48 pm
content: Out of all the cheap junk out there, the DT830-series meters (the former Harbor Freight coupon freebie) are the most accurate simple battery testers IMO. It reads out in current and specifies a "good" threshold of 4.0mA for 1.5V and 25mA for 9V. A CR2032 coin cell will read over 8mA if it is new, you can verify OCV separately. For 1.5V cells, to make fine distinctions you'd have to vary the load and threshold by size and chemistry. The default seems to be an alkaline AA cell, these are all over 4.0mA when new. Any size NiMH falls just short, between 3-4mA as does a zinc-chloride AAA. D-size Eveready Super-Duty (not alkaline) are over. IMO they've picked a pretty good fixed load resistance of 360R.

author: GLouie
author_rank: Regular Contributor
timestamp: March 23, 2025, 06:26:33 pm
content: I'd forgotten about the HFT-Centech. I dug mine out, Hah! The instructions say it uses a test load of 380mΩ!It works, but you kinda have to remember the numbers yourself.

author: BeBuLamar
author_rank: Super Contributor
timestamp: March 24, 2025, 12:28:56 am
content: Quote from: Ian.M on March 23, 2025, 04:06:57 pmGood idea Thanks. I am going to use a high power rheostat and mark the setting for each battery type.

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: March 24, 2025, 07:52:26 am
content: At the "professional" end of the market, there are some high grade computerised analysers. I have a CBA from these guys:https://www.westmountainradio.com/cba.phpMany years ago (back in the mid 1980s), I used to fly radio controlled model aircraft at public displays and made a computer controlled battery tester. It was a fairly simple tester designed for a 4 x AA size NiCad battery pack. It used a relay to switch a resistive load that would discharge a good pack over 5 hours, it used an A/D converter and plotted a graph of Voltage against time, when the cut off Voltage was reached it produced the mAh measurement. It is an easy project for someone with a spare Raspberry Pi...SJ

author: BeBuLamar
author_rank: Super Contributor
timestamp: March 24, 2025, 10:08:22 am
content: Quote from: Solder_Junkie on March 24, 2025, 07:52:26 amYour tester only good for rechargeable batteries. With disposable batteries you dispose the batteries after the test regardless the batteries are good or bad to begin with.

author: KimLum
author_rank: Contributor
timestamp: March 24, 2025, 10:40:18 am
content: If one should have a multimeter with a LoZ function, why not use that function to test battery voltage?If I test the voltage of an almost depleted coin cell with my BM789, the voltage may be measured to ~3V. Changing to the LoZ function will cause the voltage to drop down to ~2V and that tells me that the battery is not reliable anymore.

author: BeBuLamar
author_rank: Super Contributor
timestamp: March 24, 2025, 11:20:57 am
content: I do have 3 DMM's with lo Z function. Fluke 113, 114 and 289 but I asked because I don't think the tester is a good tool to check the batteries. The low Z funcion put too light of a load (3K ohms) for the 1.5V battery. Only 0.5mA. The lightest load that Energizer listed in their data sheet is 50mA.

author: MrAl
author_rank: Super Contributor
timestamp: March 24, 2025, 11:43:57 am
content: Quote from: BeBuLamar on March 23, 2025, 11:52:11 amHi there,Generally the cheaper they are the less you can trust them. However, as others have pointed out they are all only so good because they are usually only made for certain batteries of a certain size. There is a huge difference between testing an AA alkaline and a automobile battery for example, but there is not too much difference between testing an AAA battery vs an AA battery, as long as they are the same type like alkaline vs carbon zinc.The nice thing is, we don't really have to have a battery tester that can test every possible type of battery under the sun. Most of us only use a few different types of batteries. This makes it a little easier, and we can also gather our own data set as we test them as the days go by.The best load is based on the voltage and capacity. The voltage is of course measured in Volts (V), and the capacity in Ampere Hours (AH or Ah), or even in milliampere hours (mAh). Knowing these two can help choose a load size.The idea is to put the battery under enough stress so that it can show a problem but not too much so that it overloads the battery. For an example, if we have a 1.5v alkaline AA battery the rating might be around 2000mAh, and a good test would be a load that draws 100ma which is C/20 and that is the mAh rating divided by 20, which here is 2000mAh/20=100ma, and you only apply the load for a few seconds while measuring the voltage. The resistance would be about 1.5/0.1=15 Ohms.When you do this test with a new cell you get an idea what to look for. You write down the cell type and age, and the resistance you used and the voltage before and after the test. This becomes the start of your data base. Next, you use the cell in the intended application and note the hours used, then test again, then write everything down again. Once you do this a few times you start to get an idea what to look for.Car batteries are very different though because you have to have a really heavy-duty load which you can purchase and that will have the instructions on how to use it.An AA carbon zinc cell is different than an AA alkaline because it is not rated as high as an alkaline. it could be as low as 500mAh at the same voltage 1.5 volts. For this cell, 500/20=25ma and 1.5/0.025=60 Ohms, so this cell requires a higher resistance than the alkaline which was 15 Ohms.I should point out that this explanation is sort of a 'best bet' method as you can use almost any resistance to get some idea what is going on, it just may not be the best test. For example, since we know now that 15 Ohms is good for AA alkaline and 60 Ohms is good for AA carbon zinc, we might compromise and use 30 Ohms for both tests. This still gives us a decent idea what is going on. It's just important to log all the test results until we have enough results to show us what we need to know.Next, we also have to include the application sometimes. If one application draws 100ma and another draws just 1ma, we can expect to see differences in the everyday use of the cells. That's because there is another factor referred to as the "P" factor that varies between battery capacities. It means that the more we load it, the less overall capacity it will show. That means that at 100ma it will look like the very same cell has less capacity than a cell used at 1ma. This means that we need to include the application in our logs. It will show us that if we test a cell as dropping too much in voltage for one application, it may still work in anther application that draws less current.This might sound like a lot to take in, and in a way it is, because batteries are fairly complicated devices. It's not like a light bulb were if you know the voltage and the wattage you know if you can use it or not. However, doing these little tests and logging the results eventually you get a good enough data set that you can start to make really good predictions about the health of your batteries. Take the time to do some of these tests and you'll find it works really well after maybe 10 to 20 tests on a given battery type. Luckily, we don't have to test all the batteries that were ever made just the ones we use a lot.If you do these tests you can report back here some of the results and we can go farther with this if you like.It also helps to have a good voltmeter and some resistors you can use as loads. If you are interested we can go deeper into that too.

author: Simmed
author_rank: Frequent Contributor
timestamp: March 24, 2025, 11:44:45 am
content: Quote from: BeBuLamar on March 23, 2025, 11:52:11 amaccording to test standards ?i dont even know what they arehttps://www.tuvsud.com/en-sg/industries/mobility-and-automotive/automotive-and-oem/automotive-testing-solutions/battery-testing/battery-testing-according-to-un-38-3-iec-62133-iec-62619-and-other-standards