Thats roughly 416-417 days, continuous. I've only seen watches and computer clocks last this long. Neither one will use an LED as an indicator. I was initially thinking of Kai's idea, but I would not expect that the total power available would allow charging circuitry and let alone would a cap be able to hold a charge for that long of a time? Now some watches use movements to say that the battery is low (it will skip time on purpose or on digital watches might continuously blink 12:00). I have not seen advancements in pure digital watches as I prefer electro-mechanical watches, but I would imagine that they too last a very long time and they use an LCD which indicates a low power signal. According to Wikipedia's watch article http://en.wikipedia.org/wiki/Watch "Most watches with LED displays required that the user press a button to see the time displayed for a few seconds, because LEDs used so much power that they could not be kept operating continuously." Just how long does a watch battery last? http://blog.totalwatchrepair.com/2009/11/0...tery-last/ According to that information about 4-6 years. They recommend having 2 batteries for longer life. Why couldn't you use 1 battery for your indicator? Also, the only way you're going to find a changing color strip is if you can possibly change the pH by use of electricity. http://www.physicspost.com/physicsfo...D=9058.htm There's also magnetism http://www.chemicool.com/chemtalk/....php?t=822 What about those battery indicators back in the day when you could push the ends of an AA battery and the strip would go from red to green like on Duracells? http://forum.allaboutcircuits.com/newsgroup...hp?t=67806 the picture of what I am talking about http://www.otakku.com/wp-conten...rcheck.jpg