MacBook Retina 12” early 2015 battery replacement

I would contact your local Apple Store or an AASP and inquire them. please see Contact Apple for support and service

also, an OEM battery is your best bet. but being 10 years old, you might not be able to find an OEM apple battery. and they should still be willing to service the battery. but if they won't due to the mac's age, I would go to OWC’s website and ask their support team re prices. and the third party batteries they supply are the ones many here (including myself) would recommend.

Keep in mind that OWC highly recommends having a professional to install the battery since they are glued onto the underside the palmrest & trackpad which makes it difficult to remove. This forum has a lot of posts where the user accidentally damaged their laptop while replacing the battery on the Retina models.

Also, @jeffreythefrog is correct that OWC is the best option for a third party battery. The quality of third party Lithium Batteries is extremely poor so OWC is the best option....iFixIt is also an option as well. OWC does provide installation videos on their product page, but keep in mind the video makes it look a lot easier than it really is.

The MacBook you want to replace the battery is marked obsolete ,for which you can't get any spares from Apple.

It's better to Buy a new one