Battery mAH tester

[TheGizmo]

I bought a battery that was supposed to be 'brand new' on eBay for my cell phone.. OEM. Well I have reason to believe that this battery has been used significantly as it doesn't hold a charge for very long. Is there some way I can test how much mah this battery holds? This is one of those principle things. I'd pay as much as I paid for the battery to prove the guy wrong, so let me know what you can suggest.

P.S. its 9.7v and supposedly 1000 mah

 

[Heisenberg]

I don't know of any commercial products offhand, but you could make your own crude one with the appropriate resistor, DMM, and a stopwatch.

 

[FoBoT]

you have to do a load test, it isn't like you can connect something to it and it just measures capacity

 

[sager66]

New NiMH battery packs can take several charge-discharge cycles to "form" the chemistry . . slow charging is best to "equalize" the individual pack cells. If you know anyone into radio controlled models, they might have the equipment to load test the pack.

 

[TheGizmo]

hmm so theres no easy way to do it, it seems. oh well. i figured i should charge it up max then some sort of device would use the power and measure how many mah based on how long it stayed on. but i guess there is no such device.

 

[arcas]

What kind of battery? If it's a NiMH battery then sager66 is correct. If it's a lithium-ion battery then it could very well be new but just old (li-ion batteries begin deteriorating as soon as they're manufactured whether they're used or not).

You can build a crude capacity testor using a digital multimeter with a serial port and a resistor (sized so that the discharge current is about C/10). I built one a few years ago when I analyzed some NiMH batteries. Measure the voltage across the resistor at 10 second intervals until the battery voltage reaches some pre-determined "discharged" state. Use Ohm's Law to estimate the amount of current transferred during each interval. From that, it's easy to estimate the battery's overall capacity in mAh.