my battery says 84%. what does that mean? i have had my phone 2 1/2 years.ll

It means it's getting close to replacing your battery.

Batteries degrade over time with usage due to chemical aging, that's just how they work.

You can expect about a 1% drop per month with average use on an iPhone.

Apple recommends replacing it when it reaches 80%. To check your battery health, go to Settings > Battery > Battery Health.

iPhone Battery Replacement.

iPhone Battery Repair & Replacement - Apple Support

About Lithium Ion Batteries

iPhone Battery and Performance - Apple Support (IN)

Settings > Battery > Battery Health & Charging > Maximum Capacity

Is this where you see the 84% figure?

If yes, you will need to replace the battery when it is down to 80%. That might be about 4-6 months from now.