My OnePlus6T just hit 5 years old and the battery is plenty usable. I just slow charge it at night every night. Is it as good as it was when new? No. Is it still perfectly usable? Absolutely.
>>CountH+(OP)
My one plus 5t too. Absolutely working like a the day I bought it. Other than vanity and updates I don't see no reason to buy a new phone.