The continuous battle of one-upmanship between industry giants GM and Toyota continues, this time in regards to a future wave of plug-in hybrid vehicles due by towards the end of the decade. In one corner is Toyota, which will be sticking with its current hybrid system but modifying the technology to feature a household charger system. In the other corner is GM, which is developing a new, series-hybrid architecture it calls E-Flex. Already displayed in concept form, E-Flex features an all-electric drivetrain and has a backup powerplant (gasoline, diesel or even fuel-cell) that's used solely to charge the batteries.