I'd have to confirm that the light was in parallel like jtr suggested but I'm fine with playing it safe and using a protected cell even if I don't have the absolute best current from the cells due to the protection cutting them off.
I found confirmation that they're in series for this light, not parallel.
The light I linked to is not the limited edition version of that model and it's rated to go to 6800lm in what they claim as turbo mode for 2.6 hours run time. Now I'm not sure if that's just an estimate based on a typical cell capacity or if that's the limit in time that it can sustain that output without damaging the light. The limited edition does get to 7000lm and I believe you're correct that it's limited to that with a short duration. I wasn't interested in that edition of the flashlight.
The 6800lm is definitely duration limited. Look at the specs:
Mode 5: 2625 lumens / 2.8 hrs, Turbo: 6800 lumens / 2.6 hrs If you get 2625lm for 2.8 hours you can't get 6800lm for 2.6 hours. The best I could find it that it steps down after around 5 minutes.
If you want a stupid bright light to play with similar to that form factor I'd look at one of Vihn Nuygen's modifications. Like this:
http://skylumen.com/collections/v54-lights/products/tn36vn?variant=5603838980 Note, it has the batteries in series, but needs very high current batteries to power the turbo, ie: batteries good for ~11.5A, so things get interesting... Basically you need to use high current unprotected cells to get the performance, so you would need to use it carefully and not try to run it to the point where it shuts off. Of course the light is probably not very practical and is basically just a toy rather than a tool, so having to keep a rather watchful eye on the batteries isn't really that big of a deal.
As with everything it's all about what you want to do. I don't find these super bright lights all that practical myself. I have a Vihn modified BTU Shocker from several years ago. It's very bright (well was at the time, now other lights have well surpassed it) and the beam is quite focused, but it's not really a practical flashlight so I never use it. I don't find myself needing a pencil like beam with really long throw. Maybe some occasion will come up and I'll find use for it, so aside from pulling it out to impress people, it just sits collecting dust. More floody lights do get used by me, but I just can't see a 10,000lm floody light being very useful to me either.