In this work, the long term calendar Life of lithium ion cells for satellite and standby applications has been studied in experiments where the capacity evolution is tracked as a function of storage temperature. Cells containing either LiCoO2 and LiNixMyO2 positives coupled with a graphite negative were float charged at 3.8 or 3.9 V. This study focused on losses at the negative electrode and the data were fit to a model which involved a rate-determining step governed by electronic conductivity of the solid electrolyte interphase (SEI) layer, following Arrhenius' law as a function of temperature. When nickel-based positives are used, a "lithium reserve" exists on the negative and this property enhances the calendar life for long life applications.