You really don't want to only have one water purification option, especially one that is battery powered! I've drank some NASTY water in MS before with no effects. You really don't want to leave yourself in a situation where your UV light isn't working, or isn't working well enough.
What sort or water purification do y'alls keep in y'alls GeauxBag/BOB?
A quartof bleach can purify allot of water.
A whole lot!!
I use a 16oz brown plastic bottle to protect it from light, but it still breaks down in a couple months.
1 teaspoon of bleach can purify 10 gallons of water
the bleach breaks down, the bottle protects it from breaking down faster due to light exposure