Sigma's Power LED EVO illuminates dark trails. It's a super bright battery-powered headlight for serious night riding, and easily mounts on your bike or helmet. The Power LED EVO has a long run time and a whopping 900 lumens of brightness from its single high-power LED bulb. All this technology is housed in a rugged aluminum watertight casing, and this sweet light runs up to 11 hours on the included Lithium-ion battery pack.
Lead Acid batteries are the most common power source on inexpensive lighting systems. Lead Acids hold their charge for longer periods between use, which is a valuable feature for an occasional night rider. They also dim gradually during use so you'll have some light even if the battery is fading. The primary drawback is about twice the weight of the better batteries for the same capacity. Also, they typically last between 200 and 400 charging cycles, whereas superior models will last through 300 to 2,000 cycles. Lead Acid batteries will also lose more of their capacity in cold weather than the better ones.
Ni-Cads are popular because they're moderately priced, lighter and smaller than Lead Acids, less affected by weather, and are safely charged with simple chargers. A common misconception concerning Ni-Cad batteries, is a problem with "memory." You may have heard that you need to fully drain a Ni-Cad battery otherwise it will remember where you began charging it and only retain that much capacity. This has never been proven in consumer batteries or cycling lighting systems.
NiMH batteries have the best energy-to-weight ratios, are low maintenance, and have no memory effect. Even better, they offer a higher power density, which means longer run times from a super-light battery (Lithium is the lightest of all metals). Another great advantage is that Li-ion batteries cannot be overcharged. Plus, they lose only 5% of their charge a month, so they're ready to go when you (or your buddies) are. A drawback of Li-ion batteries is a fixed life cycle, independent of the number of charge/discharge cycles. This means that a 3-year-old Li-ion will have less run-time when fully charged than a new Li-ion battery that's fully charged.