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
New BLP657 Battery For OnePlus 6 Dual SIM A6000 Replacement Tool USA | eBay
SPAREWARE® OG Battery Door Back Panel Complete Housing Body with All Side Keys and Sim Tray and Camera Glass Compatible with Oneplus 3T 1+3T : Grey : Amazon.in: Electronics
Synergy Digital Cell Phone Battery, Compatible with Oneplus BLP759 Cell Phone, (Li-Pol, 3.85V, 3900mAh) Ultra High Capacity, Replacement for Oneplus Battery - Walmart.com