I try to stay away from lights that regulate like this--flat output with abrupt cutoff. Not all CR123 lights regulate this way, and not all AA/AAA lights give a warning. The MagLED AA lights are notorious for abrupt cutoff.I would definitely carry a small backup light as Styerman suggests. It only has to be something bright enough to light your way to a fresh CR123.
Like Terry said, that is a characteristic of that light, not the battery. My P1D used to give plenty of warning.