Before the + and - terminals of the battery are connected to a device there is a certain potential for electrons to flow based on the Qc value of the reaction in the battery. As the reaction proceeds and Qc changes, the potential changes. We observe this as the battery getting "weaker" (the voltage begins to drop, the "pumping" action decreases, etc.). When Qc = Kc, there is no net tendency for electrons to flow and the battery is "dead".
The other type of
redox reaction we are interested in is the opposite of the
battery type. For these reactions electrical work must be
supplied in order for a chemical change to occur. In
contrast to the battery, these reactions are non-spontaneous.
The classic example is the electrolysis of water to produce
hydrogen and oxygen. 
This requires electrical work and stops when
the work is no longer supplied. The plating of some metals on top
of others is another example, as is the recharging of
some kinds of batteries. The commerical production of aluminum
metal relies on a similar process.
