I tested the Fenix L2D with a freshly charged set of Duracell 2650 batteries. I got 2 hours 35 minutes (accurate within a few minutes) before it reverted to low power mode. That's very consistent with Fenix's stated run time of 2.4 hours if they tested with a 2500 mAh set of batteries.

2.4 hrs is 2 hours 24 minutes.
2.4 hrs *2600 / 2500 = 2.54 hrs = 2 hours 33 minutes.