I would just cut the plugs off and connect the strand to say... a weaker battery (I wouldn't suggest a car battery for this) and see how it is, but I'm a tinkerer so I don't honestly know if this will work. You could also try getting a DC to AC converter, plugging it into a battery and using that. We do that at my vocational for the LED's in the hallway powered by a wind turbine and solar cells.
Something like this - http://www.amazon.com/Cobra-400-Watt-12-Volt-120-Volt-Inverter/dp/B001RNOHBC