Small battery load test.

[tonybackache]

Wondering if there is equipment available to load test small cell batteries (D,C,AA,AAA).
Already have a battery voltage tester.

[Ed446]

Radio Shack 22-096C

[Bernius1]

All you need are a voltmeter (analog) and a spoon. You read the voltage, short the battery for about 1/2 second , and watch the needle recover. If it drops to around 1/2 rated voltage and comes right up, battery good. If it drops to 5%>50% rated voltage, and recovers to rated voltage, it's weak ( but will still take a charge, if it's rechargeable ). If its recovery slows anywhere under 95% rated voltage, it's shot. For a 1.5V (AA,C,D,AAA) battery, even low is N/G.

[jwax]

"All you need are a voltmeter (analog) and a spoon." ?
A spoon? Gotta be the nutiest thing I ever heard.
Don't try that "test" on a car battery.

[haklesup]

Substitute a small value high wattage resistor for the spoon and it will work just as well. The spoon may be safe enough for AAA-D or 9V but anything bigger may be a bit dangerous. A prolonged dead short might just destroy an otherwise good battery so keep it brief. Depending on the resistor value, you can have discharge times of several seconds or more.<p>You could also use a resistor decade box. Start by loading the battery with a large resistance. dial it down until the battery voltage is diminished. Not sure how much how much voltage drop vs load to tell you to expect, that would depend on the battery. If you have specific criteria, then one or two well chosen resistors might be enough.<p>Have you tried looking for app notes at the battery manufacturer websites. Some of them are pretty good and may lead you to a good idea you can build. There are other ways to characterize (test) batteries but may not count as a "Load Test"

[Bernius1]

Hey J !
No, I'd never short a car battery. But for 9V's , the spoon over the terminals works fine. You only have to short it long enough to drop the voltmeter to near zero, then release. All of the real information in a load test is derived from the voltage recovery. Any resistor able to sufficiently load the battery will burn your fingers, or drain the battery.
The most important quality to remember in batteries ( excepting either NiMH or Li ; one of them is linear ) is that the voltage and current curves are hyperbolic in nature. Actually, the voltage is like an inverse parabola, and the current is hyperbolic. This means that at an arbitrary point of '1/3 discharge' , the battery will show 1/2 or less current, but 80-90 % voltage. It's this relationship which demands a load test in the first place, to determine current availability.
NOW, what I personally do, with a 9V, is tap the spoon (any metal) across the terminals momentarily, just enough to drop the volts to near zero, release & repeat 2-3 times ( tap - tap - tap ). The first time is always the surface charge (like a capacitive pulse , on the plates). The next taps usually reveal a lower RECOVERY voltage. By the third/fourth tap, if the recovery voltage is steady around 90%+ of rated voltage, it's good. The surface charge effect is why automotive testers are supposed to be 'loading' the DUT for 'several' seconds.
The reason for my method is; wireless microphones can kill a 9V battery in about 4 hours. This frustrates the speaker and audience, and audio tech. If the battery was 'a little' weak, then 1 hour into the speech.....no microphone. My method prevents the embarrasment, at the expense of several milliamp-hours.
BTW, if you think a new battery can't be bad, learn to read the Spanish/Chinese/Korean/French on those grey market Duracells !!!

[josmith]

Alkaline batteries can be tested without a load. Their static volatge reflects there condition. Anything less than 1.3 volts per cell is a throw-away. <p>Carbon cells,usually called "HEAVY DUTY" don't require a tester. There good for nothing when you buy them.

[bdunne]

I'm thinking of getting the ZTS MINI-MBT to load test small batteries. I have a Radio-Shack 22-090 tester, but batteries that read good will not run my digital camera. I don't know anything about the ZTS MINI-MBT, but I'm hopeful. Any feedback about the ZTS MINI-MBT before I buy?

[Engineer1138]

What kind of a load test do you need to do? I built a 30A constant-current discharger a while back, so I may be able to point you in the right direction.