Is battery have warranty when the health reduces?

If Battery health dips to 80% or less within the first 12 months of ownership, the battery can be replaced under warranty. That is very unlikely. After 12 months, a battery replacement would be up to you to pay for.

It may differ from country to country, but check this out;

https://www.apple.com/legal/warranty/products/accessory-warranty-english.html#:~:text=non%2Dconforming%20goods.-,As%20such%2C%20the%20Apple%20One%2DYear%20Limited%20warranty%20benefits%20are,(%22Warranty%20Period%22).

This warranty excludes normal depletion of consumable parts such as batteries unless failure has occurred due to a defect in materials or workmanship and, damage resulting from abuse, accident, modifications, unauthorized repairs or other causes that are not defects in materials and workmanship.

Wafiyyy wrote:

Is this replace cost will be our own pocket money or we can claimed the warrnty for replace?

Apple will typically replace a battery under warranty that has dropped below 80% due to a manufacturing issue.

All batteries will inevitably fail, whether we’re discussing a phone battery, a vehicle battery, or a space probe; any battery.

No vendor will replace batteries outside of warranty, absent payment. If then.

Details > iPhone Battery and Performance - Apple Support

Batteries inevitably and inexorably degrade and fail. Always have, and always will. Failure is inherent in all battery technologies. When the battery health gets below 80% or so, the battery can be replaced. Or the iPhone can be replaced.