I'm assuming they are regular (non-rechargeable) batteries??? I have a few Cateye lights (EL410 & EL530 headlights, plus LD1100 tail-light) and I've definitely used them in temps below 30 (probably down to 10-15?) with no problem.
Two thoughts:
1) Try a different brand battery
2) I have heard of lights and computers interfering with one another (usually I think its the lights that put the computers on the fritz though). I have used Cateye lights & computers in close proximity with no trouble though.
Sorry, this is probably not that helpful.
Oh -- have you checked the contacts for corrosion? Made sure the bulb is tight???



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