How can i get my mac book(early 2015) air's battery replaced? Or from where should I get it?

Have an Apple Store or an Apple Authorized Service Provider replace the battery. In some regions it may be possible to mail the laptop to Apple for the repair. Click the "Get Support" link at the top right of this page to see your options.

Apple will perform a battery repair/replacement for up to 10 years now. I highly recommend having Apple replace the battery since the quality of third party Lithium-ion Batteries is extremely poor even when purchased from a reputable vendor.