Netflix movie download?

Download Netflix movies on SD Card or Internal.

What saves more battery?

Internally, because your mobile device needs to launch the "Micro SD" reader module.

I agree with the others in any case, because the device must supply the memory blocks of the SD card with additional power. But this difference is so small that you will not even notice it. That does not cost your device just a minute, because the SD card consumes minimal power. I would in your place rather consider how long you want to keep the movies on your device. For a short time it would not matter, but if it is for a long time, I would definitely recommend the SD card, because the device can never move apps completely on the SD card and you can save more space.