i've used multiple generations of Nexus devices, some more stable some less. It seems like there is always some combination of hardware, system image and installed app set that creates a situation where your battery suddenly just drains at a rapid rate.
I have seen the battery drop from what i expected 4-6 hours of life down to zero in fifteen minutes in a situation where i really, really needed the battery.
Normally you can take action if you notice this : close apps, switch off gps/bt/wifi/camera , shut down services, reboot or whatnot. The really sucky situation is when you DONT notice it and then are left with dead battery.
So, wouldn't it be nice to have higher than usual battery drain rate alert ? Havent found an app that would do this, but IMHO that actually should be a system level function.