With my Nikons I use the Nikon SD-8A battery pack, and simply fold the flap of the battery pack’s pouch, over my camera strap. I use NiMH rechargables with these.

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With my Canons I use the Canon CP-E4 battery pack, and I clip this onto the camera strap as well. Alternately, with the flash bracket that I use, I can screw the battery pack onto the vertical stem of the flash bracket. I also use NiMH rechargables with these battery packs.

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If I want more juice than that, or need to fire the strobe faster than those battery packs can deliver, I use the Quantum 2×2 Turbo battery pack clipped onto my belt.  Check this page for details about the specific connector cable for either the Nikon or the Canon speedlights.

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The advantage of the Nikon SD-8A and Canon CP-E3 over the Turbo, is that by clipping the much lighter battery pack to the camera strap, it leaves the camera bodies independent of me. That makes the cameras easier to set down, or switch them to the other shoulder.

Another advantage over the smaller battery packs by Nikon and Canon, is that they won’t damage your speedlight when you rapidly fire your flash.  The Quantum has the potential of doing that if you’re not careful.