The battery in not charging

If you mean how much is a new battery, then they are $100 dollars from iFixit for just the battery, or $110 for one that includes all the tools you need to successfully do the repair. If I were you, I would get the fix kit one (the one with the tools) as all the tools it comes with cost way more then $10 separately, unless, of course, you already have all the tools. Here's the link for the battery: MacBook 12" Retina (Early 2016-2017) Battery You may be able to find one for much cheaper on eBay, but iFixit definitely is more trustworthy then some random eBay seller.

And just as a bonus, here's the iFixit guide for the battery replacement: Sostituzione batteria Macbook Retina 2017

Good luck!