I'm using 2500mah energizers in my Fenix L2D. I did a bench test and got about 104 minutes in turbo, but the light got pretty warm. For commuting, I get at least 1 hour of run time (don't usually need more) using turbo in 15-32ºF weather. I carry a spare set of primaries and only had to use them once in the last three weeks (how long I've had the L2d), but that was because I tried discharging my cells after one commute with my maha charger (VERY slow discharge), and the cells were still charging in the morning. They didn't have a full charge so they went dead on the way to work.

Nimh cells will dump quickly when stored in the cold. If your bike is stored outside during the day, you will lose some of the charge in the cells during that time if it's really cold. If you are using a "quick charger" cells may peak (finish charging) before they are at full capacity. Batteries will also fade more quickly when used in the cold. Add all that together, and add that your batteries may be in bad shape, and you will get poor performance from any light.

Let us know how the new batteries worked out.