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
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
OnePlus 3 official: Snapdragon 820, 6GB of RAM, $399 with no invite necessary - The Verge
One Plus 3T Battery Replacement || How to Replace One Plus 3/3T BATTERY - YouTube
New BLP657 Battery For OnePlus 6 Dual SIM A6000 Replacement Tool USA | eBay