https://www.amazon.com/gp/product/B07Y9JD2F7/
These are 6×AA, but they’re 3S2P, so just sticking in one “layer” of cells will work.
Same issue like 3×AAA lights, in that they’ll be hella bright at first, but drop like a rock pretty quickly as the cells wear. So I’d probably rig up something to use USB power if I could.
Also, they’re 3-wire, so there’s “channel A”, “channel B”, and ground. That’s how you get alternating blinkies and fades and chases and whatnot. So actually they’re 150 LEDs on a string.
I intend to snip off what I might need from the end, then (if needed) reseal the end with a dab of epoxy or whatever.