An electrically driven automotive vehicle including an electric motor for driving the vehicle, an electric energy storage device for storing an electric energy for operating the electric motor, the storage device having a plurality of storage portions which can be charged and discharged independently...http://www.google.co.uk/patents/US6158541?utm_source=gb-gplus-sharePatent US6158541 - Electric motor vehicle having means for fully discharging part of energy storage device when energy amount in the other part is larger than a threshold
