Is it possible to fire a spark plug from batteries
The answer for automotive spark plugs is no with a normal battery. But with a 9v battery by stepping up the current using a ignition coil (which ramps it up thousands of volts) then you will be able to use a spark plug....Only thing with that though is that your battery (9v) won't last long, as its "Juice" will be all gone in a few shots. Hope this made sense :) just tell me if not....

You could make a spark though with your normal everyday disposable camera....Something like this: http://www.angelfire.com/80s/sixmhz/camera.html

P.S: If you used a larger battery (more volts) then you would have more juice :)