Hi, Shemyahmed!
Thanks for letting us know you want to replace your Surface Duo 2 battery.
I would like to mention that the Surface Duo 2 battery is not user-replaceable, which means you can't buy and install it yourself. If your battery is faulty or damaged, you will need to send your device to Microsoft or a participating Best Buy Service Center for repair or replacement.
You can find more information on how to get service for your Surface Duo 2 on this page: How to get service or repair for Surface - Microsoft Support
Kindly note that there may be some costs involved depending on your warranty status.
Please let us know any additional questions you may have.
Thank you!