I found the Ion was just too small. After losing three of them in a row, all within a week, I surmised that the small size and streamlined shaped makes them a natural for squirting out of pockets, pack lids and other storage spaces... I stopped buying them and just went with my Tikka.
For long night climbs, like ice climbing in the moonlight, I still use my 10 yr old Zoom w/ 4.5V flat battery cause it is still brighter than any LED lights I've tried (even though it's much heavier too) and burns for 24 hrs with no weakening of the light.