Love my Steripen. Used it, among other times, on two overnight trips up whitney, and a 9 day trip on Kili. Used a fresh set of lithium on AAs Kili, didn't have to change batteries, have used the same batteries in several shorter trips since, still kicking. (I have the Steripen Classic, which takes those batteries, the lighter Steripens take other batteries, which may be harder to replace abroad, and which may not last as long.). But if you get one, practice at home first. Have never had a field failure. I have used it at 20 degrees or less, no problem -- is why I chose lithiums for Kili (the Steripen classic can accommodate a few battery types, including AA lithiums and rechargeables, though you get fewer treatments with the latter). I do think each battery type deliveries approximately the number of treatments the mfr lists as anticipated for each type, at least in my experience.
I am, that said, kind of taken by the Sawyer squeeze filter, no batteries or moving parts, coming in at 3 oz, but don't have one myself. Just seen them in action.
