Ever since I've upgraded to GB (wiped to 5.0 and am currently running 5.1) I've been having really bad battery...sometimes it's alright, but most of the time it cant even last half of a day, even with very minimal usage.
I took a look in spare parts and it shows my phone "Time without sleeping: 100%"
I'm pretty sure this is the problem. I do have the stock kernel, but I will try another one right now to test.
Edit: Also to note, in battery status it is showing phone idle and cell standby much higher then it used to be, higher than display which i find odd.