Where does the criterion come from that a battery is gone dead when the internal impedance of a battery is over 120% of the initial impedance?
The assumption is made that the behavior of any battery that has a high impedance value is unpredictable. If you look at the graphs in the “Complete Guide” you can see that in general, once a battery’s impedance starts to rise, it keeps rising until some point at which the battery could fail open. Because batteries have many failure modes and their failure points are determined somewhat by the load placed on them, it is impossible to state exactly at which point the battery has “gone dead”.
