My iPhone battery health is depleting fast

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. This is an approximation, that is why it may be plus or minus a few percent on a month to month basis.

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

iPhone Battery Replacement.

iPhone Battery Service - Apple Support

About Lithium Ion Batteries

iPhone battery and performance - Apple Support (IN)

Here are some tips on maximizing battery life.

Batteries - Maximizing Performance - Apple

If you are using iOS 18 then you will need to refer to the beta forums as each iOS release may use a different algorithm to determine battery health.

Battery Health drops are not linear and seeing a drop in 40 days does not mean you will see that same drop in the next 40 days. On average you can expect a drop of 1% - 2% per month, with some months not dropping at all and other months dropping more. How long the battery will last before needing to be replaced when it drops below 80% depends on many factors, but if you get 2 years on the battery, then that could be considered normal.

Yes, it will continue.

If the Battery Health drops to 80% in the first year, Apple will replace the battery at no charge.

same problem,my iphone battery 99% last 7 days it’s drop 3% now 96% and if this drop will continue.

Battery cycle count 122.