Why does my Nexus One power off with 15% power remaining? Once my Nexus One's remaining power drops to 15%, it automatically powers off. On turning it back on again, it reports that it's now on 0% power.

Do all Nexus Ones behave like this, or is it just mine?

Possibly relevant apps I have installed are:


BatteryTime Lite. This gives a percentage power in the notification bar. I thought it might be mis-reporting, but the value it reports always seems to match what the phone reports in Settings > About Phone > Battery Use
JuiceDefender. This turns the data connection on and off to try to preserve battery.


I can't see settings in either of these that would turn the phone off at 15% power.

I'm currently on Android 2.3.4, but I think this happened on earlier versions too.
Probably your battery does not hold as much charge as it used to, and so your phone's estimate of 15% is incorrect; the battery is actually almost dead.  To get a more accurate reading, try the following:


  RECALIBRATION:
  
  A recalibration is mostly needed, when dealing with different kernels (ROOT!). Most custom recovery images provide the option "battery stats wipe" under the menue "Wipe".
  
  Here is how ya do it!
  
  
  Enter Recovery Mode
  do a full nandroid (or nandroid+ext) backup
  Enter "Wipe"-Menue
  do "Battery stats wipe"
  reboot
  Calibrate the battery by completely draining it until the phone completely shuts itself off. 
  Turn the phone on again and let it shut itself off one more time. 
  Then charge your phone while it is off for over 8 hours. 
  This will fully charge the battery so that when the Android is turned on, it now sees the battery as full.