  Relevant uncertainties on theoretical atomic data are vital to determine the
accuracy of plasma diagnostics in a number of areas including in particular the
astrophysical study. We present a new calculation of the uncertainties on the
present theoretical ion-impact charge exchange atomic data and X-ray spectra
based on a set of comparisons with the existing laboratory data obtained in
historical merged-beam, cold-target recoil-ion momentum spectroscopy, and
electron beam ion traps experiments. The average systematic uncertainties are
found to be 35-88% on the total cross sections, and 57-75% on the
characteristic line ratios. The model deviation increases as the collision
energy decreases. The errors on total cross sections further induce a
significant uncertainty to the calculation of ionization balance for low
temperature collisional plasmas. Substantial improvements of the atomic
database and dedicated laboratory measurements are needed to get the current
models ready for the X-ray spectra from the next X-ray spectroscopic mission.
