Rechargeable lights have come a very long way in a few years. No more bulky battery packs to mount on your bike or trips to the shops to buy batteries every few rides. The technology now available means rechargeable lights are brighter, smaller and most importantly battery life is longer than previous versions. Most lights have a range of output settings which determines battery life with most having a flash option to get you home should your battery start to run low.
The greatest innovation is the ability to charge via a USB socket meaning you can charge them via your computer or laptop, very handy if you are using them for the riding after work. Some systems still use rechargeable batteries giving you the option of being able to carry or buy extra batteries on your ride.