A higher wattage bulb will be brighter - at either voltage. Here are two examples. 10 0.83 amp 3 hrs. Coiled cords have three problems. First, they use about three times the amount of wire as a straight cord.
More wire means greater resistance, therefore less voltage to the bulbs.
Second, they tend to bounce around when you're riding off-road. We think it's best to velcro the wire to the frame and bars. And third, they typically use 22 gauge wire, which is quite thin and has a lot of resistance - particularly with 6 volt systems. We use 18 gauge wire everywhere, and you can see it in the brightness of our lights. No, but there is a recall on one charger that we supplied in some of our systems during 1993 and part of 1994.