http://gristmill.grist.org/story/2005/11/3/92411/0383#1

If VW does it, can mass production of lithium ion hybrid batteries be far behind?  Maybe even mass production of the fast charge Hitachi lithium ion battery?

That paves the way for affordable plugin electric cars that have the range and performance needed to compete with hybrids.

But the final blow to hybrids that use infernal combustion as the main power source is a plugin biofueled generator that substitutes for half the batteries in a plugin electric vehicle so that long trips without stopping to recharge become possible.

A battery pack in the trunk, for instance, that slides out and the biofuel generator slides in.  No more main oil burning power source needed.

You visit your dealership and do the swap out for your vacation trip then swap back when the trip is over.  That would leave maybe 1 in 10 cars actually needing the generator pack at any one time.

People who drive more miles than the plugin system would accomadate without recharge could just leave the generator in place permanently.