Battery pack

A battery pack (10, figure 1) comprises a thermal management (cooling) assembly 30 and a plurality of battery modules (12a-h, figure 1). Each battery module has a cooling member 31 with a plurality of cell groups (13a-d, figure 3) mounted thereon, and each cell group has a plurality of battery cells (14, figure 4). The cooling assembly has a common supply conduit 36a and a common return conduit 36b for carrying fluid, a plurality of ancillary supply conduits 35a, and a plurality of ancillary return conduits 35b. Each ancillary supply and return conduit fluidically couples the common supply and return conduits to fluid inlet and outlets (34a-b, figure 3) of the cooling member of a respective battery module. This arrangement enables even thermal management throughout the battery pack. Preferably, channels (16, 17, figure 3) are provided in each battery module, these being aligned in the battery pack to provide longitudinal channels (18, 19, figure 7) which can accommodate the common supply and return conduits and the ancillary supply and return conduits. Cell groups are preferably provided on opposing faces of the cooling member for improved cooling and space efficiency.