One possible solution is to use two solutions for your headlight. Use a dynamo and a good headlight. And get a battery-powered light. A lot of the USB-charged headlights can run while plugged into power. Check before buying. Get an external battery or maybe a few. They are lightweight. My favorite battery is the Anker Astro E1. I used to use bigger, heavier ones with larger theoretical capacities but the E1 is quicker to charge and seems to give more watt-hours per gram. I have occasionally carried two with me. You might want to carry three or four.

Even if you decide you don't want a dynamo, my recommended method for using batteries could help. And you may not need to charge anything on a 1200k.

Tail lights are easier to get right since they use so much less power.