> 
> I've wondered for years why we still use lead acid batteries to start
> our cars. Capacitance cells would be trouble when discharged but should
> charge and jump the same as a lead acid. ...I'm guessing since they
> don't have internals that will eventually stop holding charge they would
> wreck the battery market. They might fail eventually but they should
> last much longer than a lead acid battery.
> 

With a discharge time of (at most) 30 seconds compared to a lead-acid 
battery's 3 hours, ultracapacitors are no good for long-duration loads like 
running lights and radios, or starting the engine.