Bill wrote:
My flashlight shoots out photons at the speed of light and it is powered by
a 1 1/2 volt battery. Even better, my flashlight moves away from the photons
at the speed of light with the same 1 1/2 volt battery. When do I need to
change the battery?

Change the battery when it runs down to the point that your photons &
flashlight are only moving apart at about 90% of C grin.