[Q] Is my battery dead? topic

Hello guys!

I've been having battery issues for a few months now. I can barely use my phone for a whole day, without having to charge it... 6-7 hours after I unplug it in the morning.
My day goes like this:

I wake up and use my phone for roughly 20 minutes
I take the bus which is about 25-30 minutes of use
Then I rarely use it at school
A few hours later I take the bus to the gym and use it there for probably 30 minutes total
Then I use it 25-30 minutes again on the way home

When I then get home, the phone is < 15% battery. I run 100% brightness and I just use it for browsing.

I just updated to Lollipop (running stock all the way) but the issue hasn't been fixed. What can I do? It's irritating to run around with the thought of my phone running out of juice in the middle of the day.

Thanks!