Abnormally high battery drain My battery drains extremely quickly, it can deplete completely in just over 1 hour.  It can even drain faster than the charger can supply.  

Here is the battery graph after less than 60 minutes of load (this was playing candy crush saga).

Is this normal behaviour or is there something wrong with my phone?

The numbers in the usage stats don't add up to 100% either, it just says Screen 13%, facebook 8%, candy crush 4%, android system 2%, and a few other little 1% apps.  

1 year old Nexus 5 with android version 5.0, kernel 3.4.0-g88fbc66
Definitely not normal. It could be that you need to re calibrate/replace your battery. This is the ultimate solution if nothing else you try works. Otherwise I would suggest either trying different versions of Android, or switching over to a custom ROM and see if that helps.