i've done runtime tests with energizer lithium and have eyeballed the brightness with help of an LOD-CE for reference.
mine is .75 high and i get a runtime of ~50min of constant on and ~70 min. total runttime of intermittent use.
(intermittent: 5min ON, then 2-3min. OFF, repeat)
low is .50mA and i get 4.5 hours.
for high level, this is to ~50%, there is also a little more time left with lower level light.