This has greatly improved the usage of our head torches. Mine is on a full setting which gives me just over 5 hours when on the mountain bike. My wifes is set for 40 hours, medium setting for walking the dog,and my daughter has hers set for 120 hours (yes that's 5 days!)on a dim setting for messing around.
Adjustable with the easy to use software. Combined, the head torch and Core weighs less than having the batteries fitted. Plus, it saves you buying 900 batteries!!! That has got to be worth having!!