# Trying to find a practical way to evaluate a 18650 Li-ion battery...



## iasonj (Mar 23, 2017)

Far from being expert, i wonder if this can be a quick and dirty way to evaluate (used) 18650 batteries:

1. Connect a small LED voltometer in parallel on ONE cell, check the number (V1).
2. Give to the cell a certain (charging) voltage (let us say 500mA momentarily, with a small typical USB wall charger), check the number again (V2).
3. V_difference = V2 - V1.
The greater the V_difference, the worst the battery is.

Is this approach right or wrong?
I hope this is not stupid enough, but the notion under is that "the worst the battery, the greater the impedance", but i i am not sure for that! :duh2:


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## brickbat (Mar 26, 2017)

Yep - what you describe is the fundamental basis of a battery internal resistance measurement. Just make sure the 500 mA source is right at 500 mA for all cells, to keep things on an equal footing...

You could just as easily use a known discharge current too...


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## iasonj (Jul 20, 2017)

brickbat said:


> Yep - what you describe is the fundamental basis of a battery internal resistance measurement. Just make sure the 500 mA source is right at 500 mA for all cells, to keep things on an equal footing...
> 
> You could just as easily use a known discharge current too...



Thank you Jim! It is starting to make sense to me.:thinking:


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