Battery drainage on iPhone 7 Plus

I've been noticing a decrease in my battery's performance lately. I understand that's to be expected as they deteriorate over time, but it's gotten to the point where I can spend 4-7 minutes on my phone checking email or responding to texts and it drops quickly. Is anyone else having this problem with their phone? Is this a common battery issue? My battery health is at 80%. I've had 42 minutes of usage this morning with my screen brightness low and I'm down from 100 to 78. That seems like a pretty steep drop.