A system for charging serial-connected battery groups, comprising: a battery pack comprising a plurality of series-connected battery groups (1-M), at least one battery group (1-M) comprising a plurality of parallel-connected battery units (802,802a), each battery unit (802,802a) comprising one or more series-connected battery cells (81,81a; 82,82a; 83,83a; 84) connected in series with a respective battery switch, wherein: (i) the at least one battery group (1-M) comprises one or more high charge rate battery cells (81,81a; 82,82a) connected in series with respective first battery switches (85;86); and (ii) the at least one battery group (1-M) comprises one or more regular charge rate battery cells (83,83a; 84) connected in series with respective second battery switches (87;88); and a controller configured to produce a plurality of pulsed switching signals to control the battery switches in the at least one battery group, each pulsed switching signal corresponding to one of the battery switches, characterized in that during charging of the battery pack, the controller is adapted to: switch in the high charge rate battery cells (81,81; 82,82a) via the first battery switches (85;86) to partially charge the battery pack using an ultra high charging rate of the high charge rate battery cells (81, 81a;82, 82a), when a sufficient partial charge of the battery pack is achieved, switch in the regular charge rate battery cells (83,83a; 84) via the second battery switches (87;88), and select timing of ON times of switches in the battery groups (1-M) so that there is overlap of the ON times, in order to ensure that there is always at least one battery switch in each battery group in a CLOSED state at all times during charging of the battery pack, to provide a path for an uninterrupted flow of charging current through the plurality of series-connected battery groups (1-M) of the battery pack at all times during charging of the battery pack. (i) the at least one battery group (1-M) comprises one or more high charge rate battery cells (81,81a; 82,82a) connected in series with respective first battery switches (85;86); and (ii) the at least one battery group (1-M) comprises one or more regular charge rate battery cells (83,83a; 84) connected in series with respective second battery switches (87;88); and a controller configured to produce a plurality of pulsed switching signals to control the battery switches in the at least one battery group, each pulsed switching signal corresponding to one of the battery switches, characterized in that during charging of the battery pack, the controller is adapted to: switch in the high charge rate battery cells (81,81; 82,82a) via the first battery switches (85;86) to partially charge the battery pack using an ultra high charging rate of the high charge rate battery cells (81, 81a;82, 82a), when a sufficient partial charge of the battery pack is achieved, switch in the regular charge rate battery cells (83,83a; 84) via the second battery switches (87;88), and select timing of ON times of switches in the battery groups (1-M) so that there is overlap of the ON times, in order to ensure that there is always at least one battery switch in each battery group in a CLOSED state at all times during charging of the battery pack, to provide a path for an uninterrupted flow of charging current through the plurality of series-connected battery groups (1-M) of the battery pack at all times during charging of the battery pack. switch in the high charge rate battery cells (81,81; 82,82a) via the first battery switches (85;86) to partially charge the battery pack using an ultra high charging rate of the high charge rate battery cells (81, 81a;82, 82a), when a sufficient partial charge of the battery pack is achieved, switch in the regular charge rate battery cells (83,83a; 84) via the second battery switches (87;88), and select timing of ON times of switches in the battery groups (1-M) so that there is overlap of the ON times, in order to ensure that there is always at least one battery switch in each battery group in a CLOSED state at all times during charging of the battery pack, to provide a path for an uninterrupted flow of charging current through the plurality of series-connected battery groups (1-M) of the battery pack at all times during charging of the battery pack.