battery - 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.