LiPo (Lithium Polymer) Batteries are industry standard for FPV drones. They are built to be light, rechargeable, and very powerful. LiPos are rated by capacity in amp hours (aH) or milliamp hours (mAh) - (1000mAh = 1Ah) as well as rated by discharge rate (or C rating). The discharge rating is the amount of Amps or Current the LiPo can comfortably push out.
To get amps from a C rating, simply multiple the C rating by the Amp Hours of the battery. Say a battery is 450mAH and 85C - That would be (85C X .45aH ) = 38.25 Amps! This is a great way to make sure you know what rating of ESC you need.
Unfortunately, C ratings in the entire industry are misused by nearly every manufacturer out there and they cannot be fully trusted. You generally want the highest C rating you can get but comparing one companies highest C rating against another company product may be fruitless.