  We consider solutions to the linear wave equation in the interior region of
extremal Kerr black holes. We show that axisymmetric solutions can be extended
continuously beyond the Cauchy horizon and moreover that, if we assume suitably
fast polynomial decay in time along the event horizon, their local energy is
finite. We also extend these results to non-axisymmetric solutions on slowly
rotating extremal Kerr-Newman black holes. These results are the analogues of
results obtained in [D. Gajic, Linear waves in the interior of extremal black
holes I, arXiv:1509.06568] for extremal Reissner-Nordstr\"om and stand in stark
contrast to previously established results for the subextremal case, where the
local energy was shown to generically blow up at the Cauchy horizon.
