In the DJI FPV drone specs, DJI states the max flight time is 20 minutes when flying at 24 MPH in windless conditions. Assuming you’re going to be flying in Sport/Manual and in some degree of wind, you’ll most likely see flight times closer to 10 minutes.
DJI sells an add-on DJI FPV Fly More Kit that includes the following items:
If you’re planning on buying two extra batteries, this kit will save you $18 – or a total of $68 when you factor in the included battery charging hub. And the hub is probably an accessory you’ll end up buying after owning additional batteries since it makes the charging process more convenient.
More details can be found here in the DJI Store.