This is one of the main reasons I still don't have a smartphone. Battery life on an old Nokia is well in excess of 5 days, it works whenever I need it when on the road even when there are no wall sockets for miles around.
If you use your smartphone for what you use your dumbphone for it will last just as long if not longer. I have a spare Android phone I use as my on-call phone where I have data turned off and it lasts 2 weeks no problem.
edit: I used to use my dumbphone as most people use their smartphones today. It was a Sony Ericsson so it had multitasking Java J2ME support[0], a high-quality camera, GPS so I was continually shooting, tweeting, on IRC, Google Maps, Facebook etc. I had to swap batteries halfway through the day same as I do now. Not much has changed.
