iPhone 7 battery life draining terribly fast

I'm on ios 11.1 and my battery life has been horrible lately.

I had 86% battery before I went for a 20 minute walk at lunch where I increased the brightness to half so I could read in the sun but didn't turn it up all the way. My auto-brightness is turned off also.

When I was done with the walk I had 33% battery and I immediately turned the brightness so low I can barely read the screen since I had 3 hours left of work and no charger. I turned the phone on and off and then put it aside. Just picked up/turned on my phone and the battery life is at 19%, and to my surprise in the 20 seconds I looked at the screen, it went down to 17%. Just turned my phone completely off but wanted to know if anyone else has been having these issues recently? Battery life got bad when updating to 11.0 but now it's a real problem as the phone never can even make it through the day even with low use. 😟