battery tester

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danrogers

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hi all, ive got loads of aa batteries lying around that im not sure of the state of charge.

i understand that you can't really just measure the voltage of the cells under no load, so i was wondering if there is an easy way to make a little tester, that loads the cells then you could see the voltage in the cell?
 
use a multimeter
 
Transistorman said:
use a multimeter
Click to expand...
But a multimeter is not a load. Its current is almost nothing.
Measure the voltage of a "dead" 9V battery from a smoke detector. It can't power the detector anymore and can't make it beep but tests 8.5V or more (almost like new) on a multi-meter.
 
hi there bonuk and audioguru, its been a while.

I'm thinking of a cheap solution really, but that test device looks really good.

thats exactly it audoguru. What about putting a resistor across the cell then using a multimeter? if so what would be a sensible resistance to use / how to calculate?
 
The test current for an AA cell depends on what you use it for:
A 1A load is a good test for a cell that is used for a high current.
A 100mA load is a test for a cell that is used for a medium current.
A 10mA load is a test for a cell that is used for a low current.
 
thanks guru, i will give it a whirl.

would you suggest loading the cell for any set period of time before taking a measurement?
 
danrogers said:
would you suggest loading the cell for any set period of time before taking a measurement?
Click to expand...

If the current is high then even a new battery cell will have some of its life removed and you will see the voltage slowly dropping.
Just connect the load and voltmeter for a couple of seconds and if the voltage shows too low or you see it dropping quickly then either the current is too high for the cell or the cell is almost dead.
 
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