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New thermoelectric generator converts vehicle exhaust heat into electricity, boosting fuel efficiency
(www.inceptivemind.com)
This is a most excellent place for technology news and articles.
Wouldn't be powerful enough actually. You're better off having a battery that's in good condition. I've done nearly 100 km with the alternator belt off. It being a diesel, it didn't need to fire sparks though.
That's cheating :P