The invention concerns a protected system for controlling power transactions for an electric vehicle. Identification modules are incorporated into the vehicle battery management system and box, and integrity sensors of the box and of the battery are connected to a monitoring module. The system comprises a processing module for processing information produced by the battery management system, the vehicle management unit, the integrity monitoring module, and an identification module for identifying devices connected to a bus between the devices. A memory stores data indicative of technical characteristics of the battery, and data concerning events, transactions and energy depending on the information received. A calculation unit determines an energy balance according to the event, transaction and energy data. A communication module transmits a warning in case of an imbalance in the energy balance and a breach in integrity revealed by the data.