  We extend recent work of Hatsuda on the computation of quasinormal mode
frequencies via analytic continuation of bound state energies and Borel-Pade
resummation of the Bender-Wu perturbation series to the case of charged fields
in the background of Reissner-Nordstrom black holes. We compare the quasinormal
mode frequencies obtained in this manner to calculations using Leaver's method
of continued fractions, and find good agreement for damped modes (DMs) with
imaginary part remaining finite in the extremal limit. We also present
numerical evidence that the frequencies of certain zero-damped modes (ZDMs)
with imaginary part tending to zero in the extremal limit can be computed when
constructing the Bender-Wu expansion about a peak of the potential inside the
outer horizon of the black hole.
