It is my belief the L2 runtime suffers greatly from heat build-up. I say that because anytime I've just turned on my L2 and let it sit, I only get 30-40 minutes on high. However, I've had the same L2 on night hikes last over an hour (constant-on) with no discernable dimming to my eyes. The only difference that I can tell is that the L2 wasn't getting overly hot on the hikes, but when I let it sit for long periods on high in my indoor tests, it got way too hot to touch.
As long as you're handling the light, your skin helps to dissipate heat and keep the light much cooler. In those cases, if my experience is accurate, you will experience greatly increased runtimes over what test results have shown.
If you're planning on using rechcargeables, and you're feeling brave, you might consider boring the L2 to fit 17670's. I didn't know if it was possible, so I donated my L2 to science. The results were positive. Pretty simple procedure if you have some time to spare. Here's the link
http://candlepowerforums.com/vb/showthread.php?t=132443