A battery system includes high-voltage switches, including a multi-pole contactor. Multiple packs are connectable in a series or parallel configuration via the switches. The contactor includes first and second pairs of electrical terminals separated by a respective circuit gap, with respective contactor arms simultaneously closing or opening the gaps. At all times, internal switches formed by the gaps and arms have the same ON/OFF state corresponding to the circuit gaps both being closed or both being open. Two of the contactors may be used to connect the battery packs to a DC fast-charging station, and to connect electrode terminals of the battery packs to a bus rail, respectively. An electric powertrain includes the battery system and an electrical load, including a rotary electric machine, that is connected to a power inverter and to a mechanical load.