Again, for all the posters saying dynamo lights will be damaged by DC power I don't think it is the fact that it is DC that is the issue. It is the magnitude of the DC from even a small battery pack. When an AC device is presented with DC usually nothing happens! The physical construction of an AC device looks like an open circuit to DC current and there will not be any current flow unless the voltage potential is so great as to arc across the open circuit. DC battery packs don't have that huge a voltage potential which informs my opinion that the dynamo lights are DC lights albeit designed to run from a low current source of DC like the dynamo hub produces. I am not an electronics engineer, I could be off, but not too far off. The takeaway is still that it probably isn't worth the voiding of warranties and the risk of damage to the light to experiment with using batteries as power. And that is without considering the huge irony inherent in doing this since so many, many threads extol the virtues of dynamo's as a power source for head and taillights.