Nicads keep the light bright for 4 hours then dim drastically. The Night Rider makes a similar 5-Cell pack that will plug into the VistaLights. You can also get a 5W light for the Night Rider that is similar to the 6W VistaLight bulb. My second battery pack uses two 3V Lithium 'D' cells. These batteries are incredible.
Lights are critical.
We have lots of people riding, generally alone or in small numbers, on roads where drivers are not expecting to find anyone, let alone a 15 mph bike, in the middle of the night. With this in mind, lights and reflective material are a must. Headlights are important in the country side, but you actually need the stronger lights more in the towns and cities, where ambient light can make a weak light disappear into the background. When I do these things, I typically take two headlight systems. I generally carry it loose, so I can shine it at street signs or other things not straight ahead, but it's mostly there as an emergency backup.