Maximization battery lifetime and improving efficiency

Many wearable and portable devices, like personal communicators, cellular phones, laptops, are equipped with two or more battery packs to increase user flexibility in selecting the optimal form-factor/weight versus required lifetime trade off. For instance, the Compaq IPAQ PDA is equipped with an add-on module that contains PCMCIA expansion and an auxiliary battery pack. Portable and wearable computers can be powered by different combinations of two or more battery packs to give the user the possibility of choosing an optimal compromise between lifetime and weight/size. Recent work on battery-driven power management has demonstrated that sequential discharge is suboptimal in multibattery systems and lifetime can be maximized by distributing (steering) the current load on the available batteries, thereby discharging them in a partially concurrent fashion. Based on these observations, we formulate multibattery lifetime maximization as a continuous, constrained optimization problem, which can be efficiently solved by nonlinear optimizers. We show that significant lifetime extensions can be obtained with respect to standard sequential discharge (up to 160 percent), as well to previously proposed battery scheduling algorithms (up to 12 percent). From the manufacturing standpoint, numerous issues must be faced when multiple batteries have to be accommodated into the case of a portable electronic appliance. They range from the selection of battery capacities and shapes to the design of the power supply circuitry (including the switching regulator that interfaces the various batteries to the current load). One degree of freedom that, so far, has not been fully exploited, is the policy to be used for discharging the available batteries. The main contribution of this paper is the development of a new class battery lifetime maximization policies and an approach for optimally tuning the policies for a given battery system.