https://nabendynamo.de/en/products/h.../for-pedelecs/

Interesting light option coming out in July. 5W 170 lux supporting 5 to 15 V DC. No switch or tail light connection.

Aimed at ebikes, but should run off a variety of battery packs if you can find a connector to wire it up. Lack of a switch would be a little inconvenient for use with a battery.