The battery is healthy. No need to replace. When it starts showing maximum capacity less than 80 %, then consider replacing the battery.
So your issue is usage.
The phone is always contacting the cell tower and any wifi it is linked to. Normally, this does not consume much. That's how Apple and others can claim "one week on a full charge" of usage. The real world is different with the phone trying to connect to weak cell, wifi, bluetooth, etc. If the cell signal is 1 bar, the battery will be used faster. So maybe sit at a table with a window looking straight at the cell antenna

There can also be apps that are active even when phone is not being used.
If you scroll down further on the Settings, Battery page, you will see a list of apps from highest usage to lowest. So if this was a recent change in battery usage, look for a new app or updated app on that list with a high usage. For example, when i play Solitaire on my phone, it consumed 86 % of all battery usage. My battery will go from 85 % charge to 40 % charge in a couple hour session of Solitaire.
Also, to keep the battery as healthy as possible, only use an Apple charger and cable or one that is certified by Apple. Anything else, many times, will not regulate the charging rate very well if at all. For example, i have a car charger, that will charge my phone in 10-20 minutes from about 30% to 100%. My Apple charger takes more than an hour. Using quick charging or poorly regulated charging will degrade the battery over time. Best time to use it is to charge between 30 and 80 % charge, if you use it at all.
In general, avoid letting the battery get below 10-20% and more than 90% charged. Going below or above, can reduce the lifetime of the battery by up to 10 % according to Apple. Going below 10% charge is likely to shorten the battery life significantly if done repeatedly. The upcoming IOS software is said to implement further charging optimizations and controls to extend battery life as much as possible.
Your battery does not benefit from charging over 86 %. You may get a little bit of usage out of it by charging above that, but it is degrading the battery faster to do so.