I've been getting some off-camera flashes to use with all my systems (film and digital, APS-C to large format). I wanted something that could be used with an external battery, had a decent amount of oomph, and as mentioned was platform-agnostic. I ended up getting two, one as a main and one as a fill. The first one I got was labeled Calumet Genesis GF400. I got a second one sold as a Neewer. They're also marketed as Bolt VB22, Godox AD360s and Flashpoint units as well (Flashpoint is Adorama's house label). I have verified that they are all absolutely functionally identical and interchangeable. The Neewer with the larger external battery was on sale on Amazon for under $400. I had a Bolt external battery that is a bit smaller in capacity that I use with the second flash since it's the fill and therefore is usually consuming less power. The external batteries are not heavy, and they last forever. In the span of two shoots, I fired the main flash some 300+ times and the battery for it is still showing around 3/4 full charge.
http://www.amazon.com/dp/B00FFYAVC8...1460998317&sr=1&keywords=neewer+flash+battery