The disclosed embodiments provide a battery pack for use with a portable electronic device. The battery pack includes a first set of cells with different capacities electrically coupled in a parallel configuration. Cells within the first set of cells may also have different thicknesses and/or dimensions. The first set of cells is arranged within the battery pack to facilitate efficient use of space within a portable electronic device. For example, the first set of cells may be arranged to accommodate components in the portable electronic device.