Nearly every example I see of OpenGL ES involves it updating every frame, even if the image itself is not moving in any way.
I did some tests and I see it works quite fine to just render (using drawArrays etc) and then present the render buffer (these two actions, together) just once and then not do either again until you have something change onscreen.
Is this “normal” ? I just don’t see this really done much. Once drawn, the graphics stay on the screen without additional constant rendering.
Is this acceptable?
Yes, it is acceptable and completely valid. You also need to take account to render again when the context is lost. To give you an example, using Android standard OpenGL helper classes there is an option to only draw when needed, not in loop (RENDERMODE_WHEN_DIRTY).