I carry a steripen for primary purification, plus some chlorine tabs as a backup if something were to go wrong with it. I find that single-use AA lithium batter

I carry a steripen for primary purification, plus some chlorine tabs as a backup if something were to go wrong with it. I find that single-use AA lithium batteries in the steripen are very long lasting and the device itself has stood up to many trail miles knocking around my pack. Between pumping, backflushing and protecting filters from freezing I really don’t mind the reliance on batteries/electronics and the need to carry a lightweight backup. Plus I usually have a stove should it come to that.