I would first try leds as DRL's, sort of a compromise where you can run them on just with the parking lights not consuming a lot of power. In addition depending on the car model, you can remove the drl/marker light and leave the headlight intact, so you have no downtime and don't have to do a rush job in a daily driver. If you get enough brightness in the second housing, you can probably use them solo at night in traffic and only need the real headlights on a dim road.
I too have upgraded led flashlights. One thing ive noticed is you can buy 99 cent store C/D-cells and they'll live forever. The savings are very notable. I have a 3 year old.
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