The invention is directed to techniques for estimating a deformation factor of one or more capacitors in an implantable medical devices (IMD), and techniques for reforming such capacitors. An estimate of the ideal charge time is extrapolated from a first measured charge interval associated with charging the capacitor(s) to a first energy level. The actual charge time to associated with charging the capacitor(s) to a second energy level, e.g., the fully charged state, is measured. The deformation factor is calculated as a ratio of the actual charge interval to the second energy level to the ideal charge time. In some cases, the calculated deformation factor is used to adjust the timing of a future scheduled reformation of the capacitor(s).