Batteries in cold weather commuting....

As it gets near freezing alkaline batteries get weak, and if it gets cold enough they are useless. If they are not used up, when they get warm they are fine again. On a five mile commute you may be able to insulate the battery box and get a little better run time. If you get stuck on the road and they get weak put the running lights battery box under your jacket, they will return to full power. The temperature may be why they look weak one day and better the next day. REMEMBER to disconnect yourself before swinging your leg over your bike to get off. Especially if your coworkers are watching !

Ni cad and NiMh rechargeables do not get dim they just run a shorter time and then quit. This is usually better for bike lights in the cold. NiMh rechargeables are better than the Ni cad's. The Radio Shack Nimh rechargables are fine. If you charge them slower they last longer. If you can live with an overnight charger this is better for the batteries. I have a radio shack Nimh and Nicad charger that is a slow overnight charger that does AAA AA C D and 9v batteries. It was about $15.oo.

I found it is much, much, cheaper over the years to use rechargeables too.

If you use separate, but the same type of batteries for more than one of your bike lights you always can switch one set over to the headlight in an emergency. Also that charger will charge 4 batteries at a time.

It's cheaper to buy them in a 4 pack. Just a little.

However........If you do not mind the added expense of a new AA x 4 light with halogen bulb and some batteries, as mentioned it will be MUCH brighter. Maybe about $20 for a Cateye plus batteries.