On Sat, 2 Nov 2013 14:09:33 +0000 (UTC), Andrew Chaplin
wrote:

Anyone have any experience with these? I bought one last summer and it would
work fine for several hours in its flashing mode. Now that weather has
dropped below freezing, however, it runs for only about 15 minutes before
shutting off; in other words, I cannot get home with the damn thing still
working. I had been as careful as I could to fully discharge it and then
charge it fully, but that does not seem to have helped.

Temperature effects battery output, see:
http://www.discover-energy.com/why-d...ct-batteries-0

This might be your problem if your bike/batteries are kept at outside
temperatures. In cold weather.

Try taking the light (and battery) off the bike and keeping it in a
warm location to see whether that lengthens the life a bit. that
should help identify the problem.

--
Cheers,

John B.