The rolux battery adapter rl-ac40f v-mount to sony npf is designed to use your v-mount battery on a device that only supports npf. This can be useful when you already have a number of v-mount batteries and you have purchased a new device that is only suitable for an npf battery. But also when you have a device that uses a lot of power the rl-ac40f is a great solution. Application rolux battery adapter rl-ac40f whether you have bought a new device that only works with npf or you just want to change batteries less often, the rl-ac40f can be used in many situations. You place a v-mount battery on one end of the adapter and attach the other end to your device's npf connector. You disconnect the adapter easily with the button on the side of the adapter.