The OnePlus 9 and OnePlus 9 Pro may have better cameras than their predecessors, but their battery capacities will remain unchanged from last year's models. Thankfully, OnePlus will continue to include chargers with their premium smartphones, unlike Samsung or Apple.
https://www.notebookcheck.net/OnePlus-will-include-chargers-in-its-boxes-this-year-OnePlus-9-and-OnePlus-Pro-9-to-retain-4-500-mAh-battery-capacities-from-last-year-s-models.519604.0.html