I see 12v 10w cobs out there which will run off a battery, 12vdc is 12vdc, but I think you would need quite a few of them and that's before we think of faffing around charging or changing the battery regularly. Also, as the battery charge drops so does the voltage output, think of your car headlights getting dimmer and dimmer if you leave them on when the engine is off to get an idea of what I mean, which is not a good thing as once the voltage drops beyond a certain point they will just go "off" completely.
Best to use a driver or pc power supply for 12v, and a proper power supply for anything bigger, much less hassle.