Yeah, it's a bummer. When I bought my HID parts, the stuff I had read indicated the LiIon was useless in the cold, and NiMH worked better, so I went with NiMH though I'd have preferred LiIon due to lower weight. I'm not a weight weenie but if 2 things are the same cost and the one that's 2 pounds lighter works better, it's a no-brainer.
Ah well, I'm stuck with it for a few years until the battery craps out.
But FWIW, My NiMH has performed totally fine down to -5*F which is as cold as I've seen since I got it. I do charge it more when it's cold, and I bring it inside, and I don't really keep track of runtime; I have nominal 3.5 hours, but my commute is 45 minutes, I only usually use the light on the way in, and I charge "when I think of it" which is usually every 3 to 4 days, so I'm pushing it sometimes. When it's really cold I try to remember to charge every other day. Besides on those days sometimes I'm running the rear strobe in the afternoon, which draws a lot less but it does take the battery down a bit.
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