My 5500 is rather stable. I don\'t need to reboot it, though I do tend to from time to time as I\'m currently messing around with kernel modules and I want to start from fresh. Assuming you use OZ on the 5500 (which allows you to store your data on the flashROM), or you use a 5600 (which automatically stores its data on inbuilt flash memory) then you will be fine if you run out of power.
Not sure about bettery life, I think mine is starting to get worse but it still works (I\'ve had it for 2-3 years, I\'ll have to dig out the receipt for more accuracy than that, or someone can tell me when I joined zauruszone ).
I\'ve not lost any data but I perform automatic backups anyway.
I think you will need to charge more often that you currently do though.
Hope that helps a little,
Si