n64 powers on for a few secs, then restarts...

[killercottontail]

It's a lithium-ion. It has four cells. My best guess is that it's four 3.7v cells and the company are.... LIARS Another option could be that my multimeter is complete and utter crap. Whatever though it still works fine...
(Side note: At one point the battery was outputting closer to 9v but that value has gone down since...)

Here are it's innards:

[Deck]

yeah. They look like just normal 18650 cells

[timmeh87]

With those two large inductors, I would say it pretty clearly has some kind of dc-dc converter to drop the voltage. You are probably losing like 10% of your power through that.

[killercottontail]

Well in that case, I'm deeply offended!!!