POWER SYSTEM FOR A VEHICLE

A power system for a vehicle includes: a high voltage battery; a low voltage DC-DC converter configured to step down a voltage of the high voltage battery and to output the stepped down voltage; a low voltage battery charged by an output current of the low voltage DC-DC converter, where the low voltage battery includes a first cell group including a plurality of battery cells, and a second cell group connected in parallel with the first cell group and including a plurality of battery cells; and a plurality of switches configured to electrically connect or disconnect the first cell group or the second cell group with the low voltage DC-DC converter, electrical loads configured to receive power from at least one of the low voltage DC-DC converter and the low voltage battery; and a controller configured to control opening or closing of the plurality of switches.