That's what I was thinking, 2x 26650 (or 26700, is that workable?) works out to about 3C, though I don't have any 3C lights.
I'd keep looking for someone who has done this specific change. Otherwise you'd have to do a possibly destructive test (not recommended), or dive into driver details which may or may not give a solid answer.
The 3AAA zoomie I accidentally damaged had voltage applied approximately in range of two Li-ion cells (maybe higher but don't recall). I suspect some drivers working at 4.5v might be good to 6v, but maybe not much higher.
Dave