replacement of battery

Apple does not sell replacement batteries as parts. You have to let them install it if it is a supported model. Batteries offered for do-it-yourself installation are not Apple batteries. Many are low-quality knockoffs, especially those offered on auction sites.

This is the Apple support page with US pricing for battery service:

Mac Repair - Official Apple Support

Also see this from the Apple Support home page:

You do not say what exact Mac /model /year /size /retina /touchbar is this ?

DIY Battery Replacements for Apple MacBook Pro ... - OWC

otherwise take it in—

In or out of warranty you can get a free over the counter 'Apple Service Diagnostics' test /assessment

Make an appointment for a "hardware issue"—

https://www.apple.com/retail/geniusbar/