Battery Life

I use my Iphone 6S Plus very little during the day. Maybe three or four emails per day, two or three short texts and may look on internet once or twice a day for very very short periods of time. If I need to look extensively on line I use my lap top. Yet my battery level falls to 10 to 20% by mid afternoon. The battery life is at 80%. I do have some apps I rarely use on going. I have gone on line and followed some of the instructions on how to extend battery life but that has not helped. Please suggestions besides going to the Apple store. Thank you