A multi-pack battery system having at least first and second battery packs each with positive and negative terminals, and each with upper and lower switches respectively connected to the positive and negative terminals. The battery packs have a first voltage level, and are connectable in either series or parallel. A controller controls an ON/OFF state of the switches in response to input signals to select between two series charging modes, three parallel charging modes, and one or more propulsion modes. Some embodiments have a series propulsion mode. An electric powertrain system includes first and second power inverter modules (“PIMs”), an electrical load, front and rear electric machines connected to a respective one of the first and second PIMs, and the battery system. The powertrain system may selectively provide all-wheel, front-wheel, or rear-wheel drive capabilities in each of the various propulsion modes.