Battery of an IPhone 6s
My battery won't stay charged. I charge it at night, and in the morning when I take it off the charger, it will shut off, I turn it back on and it says it is at 5% low battery. Sometimes when I put it back on the charger it goes back to 100% and some times it just starts charging again.
Do I need a new battery or a new phone.
Thank you.
iPhone 6s, iOS 15