What does it mean when an iPhone dies before the battery drops down to 1%

[a-m-k]

It's the iPhone 6s. I have had it for almost 4 years. It'll be 5 this January. The capacity is at 73%.

 

[BugeyeSTI]

It needs a battery replacement... 80% is when Apple recommends a new battery if you don't want performance to be reduced or unexpected shut downs

 

[a-m-k]

Thank you. I was hoping to get it down to a single number, but I guess I can't. Since I am getting close to 5 years I might upgrade since its a little old.