I would like to Replace my battery

Apple doesn't sell nor distribute genuine spare parts to anyone, except to their Apple Stores or Authorized Service providers, sorry.

See also this support page for an estimate:--> Choose Your Country or Region - Apple Support

You can make an appointment (*) and have your battery replaced at an Apple Store or AASP (Apple Authorized Service Provider) among this list:--> https://locate.apple.com/choose-country-region .

Regards

Giulio

(*) You can do it:

• Online:--> Genius Bar Reservation and Apple Support Options - Apple;
• Contacting a local Apple Store or AASP among the list provided above;
• Using the "Apple Store" app, available and downloadable from AppStore.

iPhone Battery Replacement.

iPhone Battery Repair & Replacement - Apple Support