First, what it is: DBS (Dead Battery Syndrome) is the sudden appearance of the empty battery icon along with the camera refusing to fire. That, despite a fully charged battery. The D300 was most notorious for this, though Nikon issued a firmware fix that seems to have eradicated the problem.
I've been continuing to get reports of DBS with older cameras, most notably the D200 (though I've had recent reports with D2x and D80 models, as well). Unfortunately, it doesn't look like we're going to get firmware fixes for that. Worse still, I'm not sure the problem is completely fixed even with new firmware. Why? Well, because I have a repeatable situation with my D700 and the Tamron 28-300mm lens where I can trigger it. It appears that when the Tamron lens attempts to re-establish VR after an exposure has been taken, the load on the camera from the lens is too high and the camera shuts down. That's a real pity, as it makes the combination unusable (my other lenses do not trigger the same problem). And the Tamron 28-300mm, at least optically, is better at pretty much every overlapping focal length and aperture than the Nikkor 24-120mm that Nikon wants to sell you. But with the DBS issue, as I said, it's unusable.