Im so glad I replaced the battery on my 3+yr old Oneplus 6T. I could probably use it another 3yrs. Take it to a local shop if you dont diy : r/ oneplus
OnePlus Offers Free Battery Replacement for OnePlus 6, OnePlus 6T, OnePlus 5, OnePlus 5T, OnePlus 3, and More
BLP685 Replacement Battery for OnePlus 6T 1+6T McLaren 1+7 A6010 A6013 3700 mAh | eBay
Oneplus 6t Battery Replacement | Battery Oneplus 6t Original | Blp699 Battery Oneplus - Mobile Phone Batteries - Aliexpress
Amazon.com: E-YIIVIIL Replacement Battery BLP685 Compatible with OnePlus 6T A6010 A6013 3700mah with Tools : Cell Phones & Accessories