electron conductors while lead sulfate is an insulator. Thus, the
resistance of an electrode changes as active materials react to form
lead sulfate. This effect of change in chemical composition of an
electrode on its resistance has so far not been accounted for in
models. Resistance of an electrode varies sharply when a critical
conversion of active materials is reached and the change can be
dramatic. Measurements of Metzendorf[1] show that the conductivity of lead dioxide electrode is about 100 S m
1
at a conversion of 60% and that it drops by nearlyfive orders of magnitude
when conversion increases by only about 5%. A similar effect was
observed by Metzendorf[1] for lead electrode also when conversion increases from 70% to 75%. Metzendorf[1] used concepts of
percolation theory to propose that path for electron conduction
ceases to exist when the volume fraction of active material is
lowered to a critical value, commonly known as the percolation