Work done by all forces = Change in kinetic energy // Work Energy theorem
Work done by external agent + Work done by fringe electric field + Work done by battery force + Work done by resistive forces = Change in kinetic energy = 0
Now work done by external agent= -ve of work done by fringe electric field
Work done by battery force = EMF $\times\Delta Q = CV^2 (K-1)$
Work done by resistive forces goes in the form of heat
$\implies \text{heat produced} = CV^2(K-1) $