NiZn Batteries: Long-Term Update
The short version: When you send your SB-800 in to get its fried PC board(s) replaced, you might not wanna mention your choice of battery.
Longer version, inside.
Georgia-based photographer Russ MacDonald checked in via the comments section on the original post (which include a couple videos) on his experiences with the hyper-batts.
By the way, Russ, we won't tell Nikon about the NiZn's you have been feeding your SB-800. And no worries -- the internet is great at keeping secrets.
"Back in March, I had an SB-800 die on me right after starting to use NiZn batteries.
I sent it off to Nikon and they repaired it. I asked them what failed, but they couldn't tell me. They just replaced all the PC boards and that fixed it. After that, I continued to use NiZn batteries in all six of my speedlights for about six more months without any additional failures.
However, I decided to return to regular NiMH batteries anyway, because of one thing: The initial recycle rate with NiZn batteries is fantastic, but after about 50 to 75 shots, the recycle rate slows drastically to where NiMH is faster. This happens because the capacity of the NiZn batteries is so low. I think it is around 1200 mAHr, but it is not spec'd. The batteries deplete much faster than NiMH, and after about 200 shots the recycle rate has gotten so slow you have to replace the batteries.
With regular NiMH I get over 400 shots before they start to become too slow to deal with. The other thing I found out about NiZn is that they self-discharge very rapidly. I think faster than regular NiMH. In summary, I have switched back to regular NiMH (LSD NiMH in flashes I don't use often), for better all-around performance for wedding photography."
So, there you go.
In a couple of key ways, perhaps NiZn batteries are not the end-all. I had so far resisted the siren call of all-internal 1-second recycles, and I think I'll not be changing from my slow-drain NiMH batteries anytime soon.
Oh, and it you are into Nikon CLS, Russ has an amazingly detailed blog series about the internal guts and workings of Nikon's very capable flash cortrol system, here.