Originally Posted by
daredevil
The Cygolite NiMH Xtra has a low battery indicator. At that point you can cut back one of the lights to conserve if you'd like, either to the 6W or the 10W. I've always felt pretty comfortable with it. Again, I'll make a case for this light. Unless you have a DIY thing, this is the most light for the money that I've ever heard of. I think $80 at beyond bikes.
Although I've got an older NiCad version of the Cygolite, mine also has a low-battery indicator. It really works and is a nice feature. It has a small white indicator on top of the light that turns red when the batter charge is starting to get low. Mine can still run a good 45 minutes on the low beam once the red indicator goes on. On high beam, it will run out much faster but I'm not sure how long in minutes. My Cygolite has never actually died on my while riding although the beam has gotten noticeably dimmer.