iPhone 16 Pro Max battery health at 93% after 315 cycles

Read this support article about iPhone battery and performance to learn about the battery health feature and what is considered normal performance --> iPhone battery and performance - Apple Support

To see the feature go to: Settings > Battery > Battery Health

"A normal battery is designed to retain up to 80% of its original capacity at 500 complete charge cycles when operating under normal conditions. The one-year warranty includes service coverage for a defective battery. If it is out of warranty, Apple offers battery service for a charge." A degraded battery may display the notice: "Your battery’s health is significantly degraded. An Apple Authorized Service Provider can replace the battery to restore full performance and capacity." If it is not at or above 80% "normal", consider contacting Apple about a battery replacement. --> iPhone Battery Replacement - Apple Support

Doing quick calculation, your device is performing better than expected.

On average over longer time periods, you can expect the Battery Health to decline about 1% for every 50 Charge Cycles.

So, 315 Charge Cycles divided by 50 = 6.3%. 100% minus 6.3% = 93.7%

Your battery is doing just fine and it is right on schedule. You should be very happy.