Power wiring question.

Ok, so I want a 12v motorcycle battery on my chopper. I already have it, and I've already had it hooked up on a previous bike, running neons. Now however, I want to figure out a way to run a power wire to my ipod stereo speaker, which I have mounted on the handlebars. The speaker only runs on batteries, but I know that there's a way to run bare power wires into the speaker somehow, to allow it to run off of the motorcycle battery, bypassing the normal battery compartement. I know the voltage is likely not the right voltage and all that, not to worry, I have other speakers that are going to be used as well, which I have already figured out how to do, and have tested. All that's left is this one damn speaker, my question.... How do I wire my motorcycle battery to run my battery only ipod speaker?

Thanks guys, any help/links would be appreciated.

I'm aware of the voltage difference, I actually plan to compensate for that. I plan on hooking up 4 different speaker devices up, as well as headlight, taillight, and neons. This is why I want the big battery. I will get everything I need to properly control the voltage, but I need to know how to get an actual power wire to this one style of speaker. There is no option for plugging it in at all. It runs solely on 2 aaa batteries. I know if I open it up, and attach a positive and negative somewhere, the batteries can be bypassed, and I can hook it up to my 12v. Again, don't worry about the voltage, I'll deal with that, I just want to make sure I get proper advice with the wiring, because I don't want to electrocute myself. lol.