I've had the old school 4AA model since '05 and it has served me well. It only failed me once when, ironically, it got wet when my pack was submerged in a stream crossing and it was in an outside pocket. Apparently the UV light section is made for immersion but not the battery compartment. A couple of hours drying in the sun with the cells out and the cover off, and it was good to go.

Still, I would not take it on a long trip without a backup.
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If you only travel on sunny days you will never reach your destination.*

* May not apply at certain latitudes in Canada and elsewhere.