I have tried a bunch of tail lights including many of the ones mentioned in this thread and even some much more expensive lights like the light and motion vis 180. Over the last couple of years I have switched to using only lights (headlights and tail lights) that take AA rechargeable batteries. I always have a bunch of fully charged eneloops on hand so running out of power is never a problem. I use B&M toplights on my bikes with racks and the Relite-D mounted to the seat stay on my bikes that don’t have a rack. You can get either kind for under 15 bucks shipped from Germany so they don’t blink if that’s important to you for whatever reason. The B&M lights are guaranteed for 5 years which is another plus. I just had a B&M headlight fail after a little over a year, and the retailer sent me another one from Germany for free.