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 :)

Capacitors themselves can't step up voltages beyond doubling or inverting, to do anything else you need inductors. As mentioned previously, automobiles use ignition coils, a transformer (inductors) in an autotransformer configuration like so:

Image from "How to use an Ignition Coil [in potato cannons]"

Another possibility, though there are some problems with it, would be to just open up a circuit with some large inductance in it, which will cause high voltages (and sparks) across high resistances (e.g. a spark gap). To do this, you'd need some switch that had a voltage rating much greater than your spark gap, which may be difficult to find.

From what I've heard though, pneumatic air cannons are much more controllable, and even better, they can be triggered using sprinkler valves which work at about 24 V (I use (3) 9 V batteries)

Here's what I did, I put a spark plug in the end of the spud gun, disassembled a $10 ebay stun gun. soldered wires to the "legs" used the wire leads to the spark plug (one to casing ground metal and one to the end of the plug) push button and viola!! a few second spark!! most of these stun guns are rechargeable too so no carrying batterys!! One note of advice though prolonged use of the wire will cause burn spots and eventually lead to a short so use wire rated for spark plug use not some cheap speaker wire type stuff.