A method is provided for extending the useful life of a rechargeable energy storage unit for use in a motor vehicle, such as, in particular, a double layer capacitor, a lithium ion storage unit, a lithium ion capacitor or a NiMH storage unit, which exhibits a plurality of storage cells. In order to extend the useful life of the energy storage unit, it is proposed that the temperature and/or storage capacity of each of the storage cells be measured. If the temperature of a storage cell exceeds a reference value for the temperature of the storage cell on the storage cell is partially discharged, and, in this way, its voltage is reduced.