Just read an article about an emergency phone that has been made and holds its battery for up to 15 years on one single AA battery.
QuoteThe SpareOne mobile phone is absolutely unique - running on one AA battery, it keeps its charge for up to 15 years.
It has no camera, web browser or other hi-tech extras such as touchscreens.
It's designed simply to work as a phone - and built to last.
Read more: http://www.dailymail.co.uk/sciencetech/article-2110484/SpareOne-mobile-phone-costs-60-battery-lasts-15-years.html#ixzz1oKMLWi2I
This would be ideal for an emergency backup.
Direct link
http://spareonephone.com/
it's very nice, but £60 is a bit steep. I've an old nokia that I use for the same sorts of things they're suggesting. battery lasts at least six months, and if I wasn't near a source of electricity in that time a phone wouldn't be high up my list of priorities.