Hi Louise. If you're going to be ski-ing in the dark you'll need something with a decent main beam (but see below). But you may also want to use it for reading at night, or moving about a dorm without blinding everyone else, so it should also be dimmable or have a second softer beam. I have a Black Diamond Cosmo that fits the bill but the nature of the on/off button means it has a habit of switching on in your pocket or bag all by itself. So you'd need to check that too. I used to have a Petzl e-lite, which was very minimal, adjustable and quite brilliant, with a fool-proof switch. The main beam wasn't so great for ski-ing but it did work - usually you're not going fast and you'll be with others and their lights. I miss it but evidently I did feel the need to replace it...
I wouldn't think you need worry so much about battery life if the main features are good. The amount you'll need it on a week's tour should not be long. You could find yourself in some epic in the dark (pray not) but I feel that's a secondary thing.
TimPalmer
Although I haven't used it for ski-touring, I have found Alpkit Gamma to be light and good value for money for running and walking. Tim
JohnHare
Try Petzl Tikka RXP or Reactic - both good and stable on head for night skiing. Deals to be had on RXP at moment as Reactic is replacing it.
AndrewKydd
Hi Louise. If you're going to be ski-ing in the dark you'll need something with a decent main beam (but see below). But you may also want to use it for reading at night, or moving about a dorm without blinding everyone else, so it should also be dimmable or have a second softer beam. I have a Black Diamond Cosmo that fits the bill but the nature of the on/off button means it has a habit of switching on in your pocket or bag all by itself. So you'd need to check that too. I used to have a Petzl e-lite, which was very minimal, adjustable and quite brilliant, with a fool-proof switch. The main beam wasn't so great for ski-ing but it did work - usually you're not going fast and you'll be with others and their lights. I miss it but evidently I did feel the need to replace it...
I wouldn't think you need worry so much about battery life if the main features are good. The amount you'll need it on a week's tour should not be long. You could find yourself in some epic in the dark (pray not) but I feel that's a secondary thing.
Good luck,
Andrew