To upgrade my battery
How do I upgrade my battery life span to prevent me from unexpected shutdown
Question marked as
Which iPhone do you have?
Are you able to go to Settings > Battery > Battery Health? If so, can you provide a screen shot or tell us what it says? Specifically, what is the Maximum Capacity?
You cannot upgrade you battery but you can have it replaced. The link is below but please answer my questions so we can determine if it is worth paying to replace your battery.
iPhone Battery Repair & Replacement - Apple Support