These batteries are a perfect match for any Sony camera that uses the BP-U form factor, including the FX9, FX6, FS5 and FS7. On an FX9, you can expect roughly 2 hours per battery. On the FX6, FS7, or FS5 platform, you'll get approximately 3.5 hours per battery.
Because they are so stout, they also offer a p-tap port for powering accessory items. You'll also find a USB port (with regulated 5V power).
This kit includes 2 of the BP-U65 batteries and a dual-slot charger that conveniently charges both batteries simultaneously.
For the number-curious among you, each battery is nominally 14.8V, with 5200mAh of power.