SYSTEM AND METHOD FOR BATTERY PACK

A battery pack comprises series-connected battery groups (1-M). At least one battery group comprises one or more high charge rate battery cells (81,81a; 82,82a) with first battery switches (85;86), and one or more regular charge rate battery cells (83,83a; 84) with second battery switches (87;88). A controller (2) produces pulsed switching signals to control the battery switches (85-88), each pulsed switching signal corresponding to one of the battery switches (85-88). The controller partially charges the battery pack (1) using an ultra high charging rate for the high charge rate battery cells (81, 81a; 82, 82a). Then the controller switches in the regular charge rate battery cells (83,83a; 84) via the second battery switches (87;88). The ON times of switches (85-88) overlap, to ensure that there is always at least one battery switch (85-88) in each battery group in a closed state, at all times during charging of the battery pack (1).