http://www.valence.com/default.aspThey make 2 different flavors of their batteries the N-Charge and the N-Charge II
I own 2 on the VNC-130's and they are great. The only thing I don't like about them is the adapter that connects the battery to the Lappy. It doesn't lock in to place. I use 2 large runbber bands to secure them. Anyway I haven't tried the new units, they look like they might be built a little better than the orignals but as I said I dont have any hands on experience with them.
With my laptop I get about 3.5+ Hours per 10Hour(x2) battery while taping. They get the job done. If your laptop supports running 2 internal batteries I would go that route as it will be cheaper. You could also check to see if the internal batteres in the laptop are HOT swappable (meaning you can remove and replace 1 w/o causing the laptop to shut down).
I run 2 Internal laptop batteries and have the 2 10hour N-Charges so I usually never worry about power