Tried the battery trick. Its really not as good as you think it might be. A small 5ah scooter battery will run a smart phone via a usb adapter for about 12 hours with the screen on. Thing is it takes up more space than its worth. I've switched to liion cells with a charger/discharger and a solar panel. Then I use 300 lumen torches on the bars that use the same cells. I get gadget charging, off the grid capability, and batteries I can use as a light source if I want to. Its been bouncing around in head to take a bottle dynamo, mount it to the brake track (I use discs) and draw power from there. But, I think its easier just to get a hub dynamo.