The analysis of telemetry data of the Argentine electricity storage system SAC-C satellite is presented. Diagnostic indicators were established in order to evaluate the in-flight performance of the satellite nickel-hydrogen batteries. The state of charge of the batteries was related to the hydrogen pressure. A predictive analysis allowed us to detect early failure of the electricity storage system. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.