Recently (so recently they haven't arrived yet) bought a couple of Cygolite Metro 800 Lumen lights. Have been using MagicShine 908's exclusively for the last 10 or more years. Have at least four lights and two battery packs. Batteries are by Gemini. There isn't any getting around it, a 4 x 18650 battery pack CANNOT be made into a helmet light. It has to be external. All in one helmet lights will be 2x 18650 and thus will have 1/2 the runtime. Which may be fine. Cygolite Expilion's allow you to carry 2x18650 removable packs for extra runtime. I decided I didn't need that and will charge every night.