Electronics > Beginners

How to measure the mAh capacity of AA/AAA NiMH batteries using a multimeter?

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gwet:
I am trying to measure two AAA batteries of 600mAh each. Plugging the probes into the COM and 10A input jacks gives me a reading of 1 and 1.4 amps respectively.

I know I am doing something wrong...... and I would probably have blown a fuse if I had plugged one probe into the mA input jack...

Simon:
You can't measure the mAH like that, you are short circuiting the battery, you always measure current by putting the meter in series with the load,to calculate the mAH of the battery you should discharge it and measure the current until it is empty and then work out how much current came out of the discharge period

Zero999:
Lol your measuring the short circuit current of the batteries not their capacity and are lucky it wasn't high enough to damage the meter.

Simon:
I did the same with my first meter, one of the reasons in the other thread I recommended a 10A meter as a first meter

Psi:
If they are 600mAh batteries then that means they can theoretically supply 600mA for 1 hour.  You can't test this by just touching a meter (or any other test gear) on the battery for a sec and taking a reading. There is no way to know how much energy is in the battery other than to discharge it and see how long it takes.  ie, connect the battery up to some load, like a light bulb, and record the current readings at regular times until it's flat. Then you can work out what the capacity of the battery was using the current readings and the length of time it took.  If the battery was fully charged when you started then you have worked out the maximum energy the battery can hold which is what the 600mAh written on the battery means.

If you just wanted to see how 'good' the battery is then set the meter to volts and take a reading. 1V=flat  1.5V=full  or 1.25V=good (if it's a rechargable battery).

Sometimes people do connect *small* batteries up to a meter on the 10A scale for a fraction of a second to see how charged a battery is. However it's a very bad habit as it's not all that good for the battery and if you ever did it to a big battery your meter would probably explode, or at the very least blow the fuse. (even a little AA can supply over 10A if it's a good quality one and fully charged when shorted out)
The readings you get when you do do it are a combination of how much current the battery can supply under extreme and ridiculously high load and the batteries internal resistance. Because the battery is being pretty much shorted out the voltage is so low that the readings are pretty meaningless except to compare with other batteries tested the same way on the same meter. Different meters will give different readings as they're not really designed to measure current at such a low voltage.
So, long story short.... Don't do it, its bad :P