I don't think lights are an either/or they kinda work in pairs.
I would go with rear light if I somehow was stranded with only 1 battery and a pair of lights. Not as the front is less important but I will be in a position to make my own actions about what's ahead of me(until I hit a random pothole I can't see till it's too late). Ride slower and approach all junctions/turns like someone will pull out without warning. When/if I do stop hopefully the driver behind can see the rear light.
If you have forgotten/lost a light poundshops dotted about will usually have something.
I don't think lights are an either/or they kinda work in pairs.
I would go with rear light if I somehow was stranded with only 1 battery and a pair of lights. Not as the front is less important but I will be in a position to make my own actions about what's ahead of me(until I hit a random pothole I can't see till it's too late). Ride slower and approach all junctions/turns like someone will pull out without warning. When/if I do stop hopefully the driver behind can see the rear light.
If you have forgotten/lost a light poundshops dotted about will usually have something.