Close all applications, open terminal and then use ps (or top/htop) command to list all processes. Watch the listing to spot any applications that shouldn't be running. (those apps that you have installed yourself and have recently ran) Exception to this are prestarted stock applications like grob (the default web browser) which are always there and automatically restarted if killed.

For example if fennec (firefox) is listed even if not open, then you know it has crashed.
does the trick and force kills it.

You'll soon find out the usual culprits and in the future can simply filter ps output for their names to quickly see if they have crashed or failed to close. For example:



To monitor your battery usage you can use graphical Battery Usage app http://store.ovi.com/content/138659 and power analysis tools installable from developer mode menu in the Settings application. From command line you can use powertop and bmestat.