The battery is good. I've had mine since launch in 2018 and have never experienced excessive battery drain, but then again I don't install any sketchy third party software.
Typically record 5-10 hours of activities per week, plug it in roughly once a week when it reaches 20%. (I could probably get another couple of days of battery if I wanted)
My 5s Plus is 1,5 years old and I have to charge it once a week when I don't work out and every 5 days when I run 3 times a week for an hour. During hikes I record 8-9 hours and it still has 20% left. I'm happy with it.
