I got the IR version of the Pak-Lite to use with my IR monocular at night.

It weighs in at 50g (1 3/4oz) with the Duracell alkaline 9volt battery, 54g with the strap. Wouldn't the lithium weigh less? They also say the lithium battery works in sub-zero temps, which implies to me that the alkaline won't. Not that that is a problem here.

They advertise burn times for the IR light of
Duracell Alkaline=75+ hrs. high, or 600+ hrs. low and
Ultralife Lithium=200+ hrs. high, or 1200+ hrs. low

I'm serously considering one of
these for backpacking. It also has a 3-way switch of 1led-off-2led's.

That one is advertised as
Duracell Alkaline=30+ hrs. high, or 600+ hrs. low and
Ultralife Lithium=80+ hrs. high, or 1200+ hrs. low (sold separately)

I assume the white light led's are within a gram or two of the IR led's.

(PS - I forgot the "headlamp" qualifier. Oops.)