And yet, most of the electric cars and PHEVs on the road right now, whatever their range or 0-to-60-mph time, depend on a relic to get moving: a 12-volt battery, usually of the lead-acid variety.

This requires the Volt’s drivetrain—composed of two electric motors, a gasoline engine, three clutches and a planetary gearset—to blend power from different sources to find the perfect ...