During the military shoot on Oahu a few months ago, I tested out the new Paul Buff Vagabond Mini Lithium battery pack that I had rented from Photographics Maui (if you are ever on Maui and need to rent photo gear, they are a great resource to check out).
The Mini Lithium battery was a real powerhouse, lasting almost the entire day doing full power shots on a WL1600. It's much more compact and lighter than the older Vagabond II that I had been using before, and lasts a lot longer.
Because it's so much lighter, you can't rely on using it as a weight to hold down your lightstand like you can with the older Vagabond II.
The spare battery packs are easily swapped out and are not too expensive.
One thing I didn't like about the VML is the design of the clip that is supposed to attach the battery to the lightstand. Not the greatest design - in actual use when you clamp it onto a lightstand, it tends to slide down until it hits one of the joints of the stand. Hopefully they will improve this in later versions.
Paul Buff also sells a carrying bag for the Vagabond Mini, which can also hold a spare battery.
Putting both the Vagabond mini and a spare battery pack in the bag gives it a little more weight to help hold down a lightstand, but it's a good idea to supplement that with one or two sandbags, especially if you will be using any softboxes or other light modifiers on your strobes.
One future application that I'm planning for this is using it to power LED light panels when shooting video. In testing it with four HDV-Z96 LED panels, it seemed to hold up pretty well. Will need to do a stress test with it to see how long it can last without anything blowing up.
Overall I'm really happy with the Vagabond Mini Lithium - it's lightweight and lasts long. It's also very affordable, to the point where I'm seriously considering getting a few more of these - one for each lightstand.