My phone battery percentage never seems to be right. It’s an iPhone 6s Plus. Between 40-80% it seems to drop off suspiciously quickly. Above and below it seems to mostly drain at a normal rate.

For example: I charged it up before the dog park to 90ish percent. I started streaming radio and put it in my pocket. Took it out and started doing some browsing of oppo and other Kinja sights after about 20 minutes. Phone was at 25%. Continued streaming and browsing. Watched some YouTube when I got home to wifi. Used it for navigation. It sat at 23% for about an hour and has been at 22% since. So in 3 1/2 hours it’s gone down 3% but in 20 minutes went down almost 70%.

Should I let it drain till it dies and then charge back up? Restart? Something in settings?