Bontrager’s Flare 3 Taillight is ridiculously bright, which is exactly what you want. It's got 2 standard red LEDs and 2 super-bright, .5-watt, ultra-bright LED that are visible for up to a mile! It's got a 30+ hour run time, steady and flashing modes and includes mounts for attaching it to your bike, pack, belt, wherever.
2 AAA batteries are included.
Run time: 30+ hours