I don't have dynamo power, so yeah my main preferred tail light is battery-powered. Specifically, the
Cateye Reflex Auto. I also carry a spare set of AAA Eneloop Pros, which I have never needed to use even on 1000k rides. This is for constant illumination though - for blinkers I still use USB rechargeable lights like the Cateye Rapid Mini, and the Rapid X3 mentioned above, since they already have phenomenal battery life in blinking mode (though that may not be a feasable option depending on your country's laws on blinkers).