Testing Batteries?

[DiodeDude]

Hi:

I'm just wondering if anyone knows what is a reasonable resistance to put on regular household akaline batteries for the purpose of testing them with a digital meter. I know a battery can sometimes read 1.2-1.4 volts with no load..... But when you put them in a device there is not enough juice to run the show.

Any Ideas/ Suggestions appreciated

TC
DD ½

 

[rezer]

Hi:

I'm just wondering if anyone knows what is a reasonable resistance to put on regular household akaline batteries for the purpose of testing them with a digital meter. I know a battery can sometimes read 1.2-1.4 volts with no load..... But when you put them in a device there is not enough juice to run the show.

Any Ideas/ Suggestions appreciated

TC
DD ½

You could load them with a resistor, but you could just as well test it in an alarm or anything that uses one. This is how I typically test them. Plug them in and test with a meter. But if you want to go with the resistor, it depends on the AH rating. You could supply a load that matches the AH rating of the battery, but then this may only indicate that it is drained but still able to supply enough power to operate a device (Consumer products that work off of a 9V battery don't draw anywhere near the AH rating). Match it against the usage of the product that provides the heaviest load, then it will work in anything.

 

[Torben]

I wonder if this might work:

If possible, download the battery's datasheet from the manufacturer. I know that Energizer and Duracell publish these; I don't know about other makers. The datasheet will usually have a chart on it plotting voltage against time for one or a few different loads. Use a resistor network to present one of the given loads. While the battery is feeding that load, read the voltage on the battery. Plot that value on the chart and it should tell you where on the discharge curve the battery is.

I haven't tested that and just thought of it now so I haven't even really looked for holes in the idea. I'm sure there are some but it seems like a good way to get a rough estimate. The flatter the discharge curve of the battery, the rougher the estimate, though--so some battery types would be easier to measure than others if they were somewhere in the middle of their discharge curve.


Torben

 

[rezer]

I wonder if this might work:

If possible, download the battery's datasheet from the manufacturer. I know that Energizer and Duracell publish these; I don't know about other makers. The datasheet will usually have a chart on it plotting voltage against time for one or a few different loads. Use a resistor network to present one of the given loads. While the battery is feeding that load, read the voltage on the battery. Plot that value on the chart and it should tell you where on the discharge curve the battery is.

I haven't tested that and just thought of it now so I haven't even really looked for holes in the idea. I'm sure there are some but it seems like a good way to get a rough estimate. The flatter the discharge curve of the battery, the rougher the estimate, though--so some battery types would be easier to measure than others if they were somewhere in the middle of their discharge curve.


Torben

Yes, but I didn't have any luck on Duracell's web site. I gave up after a short look. I did find one on Energizer's for a 9V alkaline.
https://www.electro-tech-online.com/custompdfs/2008/09/522.pdf
It has a voltage vs. time graph for a 620 ohm load that would be a good test.

 

[Willbe]

Collect all the A-h ratings for all the sizes of alkaline batteries you want to test.

For a battery with a 20 mA-h rating the "C rate" is 20 mA. For a 2000 mA-h battery C = 2 A.

Make up a resistor network with selector switch that will load each of your batteries to, let's say, the C rate.

Once you get a reading on your meter for one slightly discharged battery take that same battery to a store that has a commercially built battery tester and see what it reads.

If the store meter reads 70% of full scale and your meter reads 90%, shunt some current away from your meter movement so your meter now reads 70% or use a lookup table, and hope that all the other battery size load resistors in your meter will translate by the same amount as the resistors in the commercially built battery tester.