Surprisingly, I have resisted the iphone / android trend and am happily using my old N73.
It seems its battery life is superior to other phones. I often use it for hiking with a UK hiking map application that allows you to see where you are on OS maps. I used a bluetooth GPS unit that is small and lasts for 72 hours.
My questions is: are there any nokia s60 phones that have better battery life than the N73 which can also run my mapping app? It seems that modern phones do not last long. I think having external bluetooth GPS helps because most phones use inefficient gps chips.
I'm tempted to get a spare n73 on ebay just in case mine days, so I'll still have a reliable and long lasting navigation solution that doesn't die after a few hours, and which can have spare batteries.
I have also noticed that my BP-6M cells need replacing, they are getting old. I wrote a script in python s60 to record the battery life of each battery, so can compare them using that program. Also a nice way to spot genuine ones from dodgy ebay ones!