How build a decent battery tester?

How can I build myself a decent battery tester for domestic use? Are there any circuits? Any info about off-the-shelf equipment? (I am in
the UK).
Of course I don't want to spend more cash than I save in batteries, so there is a limit budget.
At the moment I use an ordinary digital multimeter which has a setting to put the cell under a load of approx (a) 10mA or (b) 150 mA.
At present the *main* cells I would like to test are AAA and AA cells made of NiMH, NiCd, manganese-alkaline or zinc chloride
I would like to have a device which simultaneously shows the current and voltage of a cell under load. And then it would be useful to simulate different loads - perhaps using a variable resistor?
If it's not too hard to also get a display of the internal resistance of the cell that I'm told that can be useful. I gather that internal resistance of rechargeables can show the battery's state of health. However int resistance increases as the theoretical max capacity increases and I guess this means that absolute calibration is not possible, however perhaps internal resistance varies during charge and is an indicator of capacity?
Thanks for any info.
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Alex Coleman wrote:

a DVM, note pad, and a resistor you likely already have !
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Alex Coleman wrote:

"Testing" rechargable batteries is a waste of time. http://groups.google.com/group/sci.electronics.basics/browse_frm/thread/9c63b18dae7e639a/cb67cf01392ff5c2?q=the-voltage-holds-up-right-until-the-battery-is-discharged+recharable http://groups.google.com/group/rec.photo.digital/browse_frm/thread/90feb3b5c1e17df/d382bd70a1e188f2?q ttery-Tester+rechargeable+flat-discharge-curve+NiCd+NiMH
To test a disposable battery: 1) Measure the no-load voltage of the cell. 2) Measure the voltage when loaded with a resistor (~10 ohms). 3) Make a chart of what is a "good" reading (correlated to real-world failure of your battery-powered devices).
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Alex Coleman wrote:

What's your objective? The whole idea of batteries is that when the thing stops working, you replace them. For critical items, you use NEW batteries and change them on a schedule determined empirically.
I use a computer, GPIB programmable power supply and programmable load. I've found two useful measurements. Lithium ion rechargeable batteries fail with high internal resistance. The electrons are still in there, but the device shuts off due to low voltage and won't let you have them.
I built a tool for sorting lithiums at the surplus dealer. 8 AA nicads in series. A car tail light and switch in series to the test leads. DVM across the test leads. Measure the cell voltage. Under two volts, probably scrap. Close switch and charge the cell until the dv/dt slows down. Measure the voltage, let go of the switch, measure the voltage again. Difference is related to internal resistance. You can do the math and get a number, sorta, but experience over a few dozen cells compared to a new cell is your best teacher.
Second useful thing for nicads is to plot the voltage while charging. The curve shape of a good cell is unmistakable. Ditto for discharge. mike
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finger to keyboard and composed:

I use Bob Parker's ESR meter.
See the table of battery ESRs at the bottom of this page: http://www.flippers.com/esrkthnt.html
- Franc Zabkar
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Franc Zabkar wrote:

A $80 *kit* to test dead batteries.
Capitalism at it's best ...
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Alex Coleman wrote:

One thing that rechargeable and alkalines have in common that they have high impedance when close to discharged state. So cheap and easy (partially distructive though) test is to use a multy-meter, switch it to current measurement mode and using a high-current path (10A), short the cell momentary. If you see a sustained current (usually 3-4A but it is not important) than cell is OK. If you see current drop very fast to below 1A, cell is close to dead state. Yes, you will lose some charge while doing this test, but for that you don't need any additional equipment, even no resistor. If you happen to have a 1 Ohm resistor, you can use it instead of the short. Procedure is the same but current will be much less.
Regards, Yevgen
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A variant on that that can be revealing is a very brief short-circuit, about a tenth of a second, then watch how the voltage recovers immediately afterwards. It might not reveal much, but probably enough to allow less time at heavy current.
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