Dunno. What powers them now? (Google failed to return any technical information.)
They are PC speakers so it has an amp that plugs into an outlet. You would need some kind of inverter like what you find for cars to convert 12v DC to 110-120ac. I think... I'm not an expert on this.
DIY Sound Group: Information and Tips
What are your goals -- cost, size, weight, convenience, do you already own the speakers or battery, what are you going to use it for? Depending on your goals, you would likely get better results and spend less by purchasing a commercial battery powered speaker system.
I think it is almost certainly a bad choice, but you can run those speakers off a battery. Not a single cell phone battery, though. (*)
Those speakers plug directly into the wall (see http://www.cheatengine.org/forum/viewtopic.php?p=4996392&sid=4a4556ab8e9f314194fd645007e9c090). Inside the speakers, the wall power is converted down to low voltage DC. But you would have to open them up and rewire them to run them from battery, or use an inverter (like Mrkazador suggested) with a big battery.
Batteries also produce low voltage DC, but you'll need to get a battery pack with the right voltage, or at least close, if you rewired the speakers to run from a battery. Battery capacity is important, too, as you don't want it to run out of battery in 5min. You'd also need a charger.
So, though it is technically possible, it is totally impractical to run those speakers from a battery.
(*) Actually, even that is possible with a boost regulator or a new amp, but it's a terrible idea for any set of goals other than an evil madman is holding you hostage and requires that you make this work at any cost or he will injure a puppy.