Quite new to Maya, so this is most prob a stupid question ...
I have created an animation and used the "Display Render Settings" window to change the background, under mental ray> environment> image based lighting. Changed it from image to texture and created a bright blue background. Now, when I preview a frame in the "Render View" window everything is perfect, but when I render out the scene using the Batch Render option, all the frames have a black background.
That's because maya is adding an alpha channel to your render images, you can always add a background in another app like after effects or you could disable the alpha channel in the render globals window under renderable cameras there's an Alpha Channel (Mask) toogle.
Although if using Mentalray I think you need to actually go into the Mantalray render globals tab and go down to the obscure "frame buffer" area to set what channels to output. For rendering with the regular Maya renderer it's more obvious, just toggling off the alpha channel option.