Hey, Ive got a Sony HVL-20DW2 20-watt Video Light. The reason i got this particular light is because it use the same as the PD170. I then bought two Sony NP-F970, L-series batteries (you should get at leas one for your camera) I use the small battery that came with the camera as a back up. I shot a wedding last Sat and used one of the fully charged bigger batteries and it lasted me roughly from 5:00 to 12:00 but it was completley dead when i was done. When using a light (in my experience at least)they use a lot of juice so you want to make sure you have plenty of extry batteries.
http://www.bhphotovideo.com/ is the best place (imho) to get your gear. Also feel free to call them up and ask questions. Most of them are pretty knowledgable and can help you out with specifics. Im not sure which light you have so I hope this helped some. Good luck.