I got me a new fancy battery charger that measures the internal resistance (if that's the right term) of the battery and I am trying to learn how this works.
My current understand is a higher internal resistance means the battery will still work but it might not be able to provide enough power if the device draws more power. The fire alarm might look fine for example, since it needs little power, but it might not sound in case of a fire since the battery's internal resistance prevents it from providing enough power.
I am testing some old and new rechargeable batteries and indeed, my new AA battery has a 27mR (new eneloop) and the old one shows 127mR (years old Energizer). Meaning the old on has a higher internal resistance. Correct?
Now, I suppose the old one is so old I should throw it out but how do I know where to draw the line? 30mR might be really good but is 90mR? What about 100mR?
In short: how do I know at what threshold a battery should be considered "dead"?
I looked at the datasheet of the Energizer as proposed in the comments. It gives a "Internal Resistance" of 100 milliohms for a charged battery and an "Impedance" of 35 milliohms for the same charged battery. Which one is the the number I need here?
If I take the 35 milliohms the battery would be good if it read between 28 and 42 milliohms (+ and - 20% as shown in the sheet). Do I get this right?