Wow. What a timely thread--I was just thinking of starting one up on this subject for two elements. And those are...
Have you tried this Andrew? I had an old cell phone battery, but when I went to look for it to try this experiment...well, I dunno what the heck I did with that battery.

It should work in theory, but I don't know that you get a long enough drain time with a cell phone battery given its low discharge design. Would love to hear your experiences with this.
This actually is what I wanted to ask.
I've seen
a lot of survival texts
talk about using a battery to start a fire... and they all show a 9V touched to steel wool. Yeah... yeah, that can work. I think there was some good advice here that it doesn't cause the rip-roaring bonfire that some books make it out to sound though--my experiences here have been a small glow with typical steel wool. You still need to transfer the ember to tinder to get that glow into a real fire.
But a few of these same texts also recommend using "any type" of battery, and simply using "wires" to the + and - terminals to generate the spark.
Okay, but those
better be insulated wires.
You don't want to hold bare copper and connect even to the smallest AAA battery, or you'll get a severe but tiny burn in about 2 seconds.
Use wood, please, to hold bare copper wires! No, you don't get electrocuted from a AAA, AA, C, or D battery... but you will feel fire in your skin almost instantly!