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Many portable devices, like laptops and PDAs can be powered by different combinations of two or more battery packs to give the user the possibility to choose an optimal compromise between lifetime and weight/size. The common discharge policy for multiple battery packs is sequential, i.e., the system switches to the second pack when the first one is empty. In this work we demonstrate that this policy is not optimal by proving the effectiveness of two other policies, namely switched and series, which significantly extend battery lifetime, but require some additional control circuitry. We present a complete implementation of the power supply circuitry and detailed measurements on battery discharge times. Significant lifetime extensions (20 to 30 %) have been achieved for dual-battery systems under high current load.
Bruni et al. (Tue,) studied this question.