Riding mine in the dark this morning I decided to run it on low a bit, a lot of people run lights like this anyway, and some even use it on the magicshine going "its more than enough for the road", but comparing Low to the High mode makes Low suck, and I use high almost everywhere there isn't street lights (95% of my commute).
2hrs+ is easy on high, you should be looking at 2.5hrs, although if you drop it to low at the 2hrs mark you should have another 1-3hrs in low.
I think I'd prefer a longer runtime than that. Okay for commuting if you get into the habit of sticking it on charge every (other) day but it'd be a limitation for my purposes.
Btw, I do know this thread is in 'commuting'!
You can use the low mode for more than 2x the run time, you do have to balance it against though and you're not going to get much longer really without different cells or a more efficent LED.
It is possible and very easy to build extended battery packs etc, with lithium (as used) or just regular nimh.
Also, even off road or on longer rides, how long do you actually ride continuously without stopping? even for 5 minutes? get a second battery pack and switch them over at that point
