i had that issue before ever since i went to 6.5. but now whenever i'm not using my phone weather i'm work or not i check my taskmanager to make sure nothing else is running and then i put my phone in sleep mode using xda power-off manager thingy lol (i forgot the actual name) but it does wonders for you! i did a test drive using this method at work and my phone being at 97%. every now and then i would check my phone for any messages or making calls and then i would put my phone in sleep mode. then after a 10 hr day at work i go home and check my phone and my battery is still well above 80%! and then i would play smartgear and drain the rest of the battery out before charging it up again hahaha!
Edit: my process usage is stable at 60% whenever i use my phone but whenever i do a soft-reset it goes down to 50% then goes back up to 60% i wonder what that 10% of usage is? hmm