Here’s some reveiws and comments from one of the best the community has.
Batteries with ridiculous ratings
Disassembly of some UltraFire batteries
FWIW, I got an Ultrafire with a light. It claims to be 5000mA. When I finally got a charger that could test capacity it came out at 850mA. I use it as a ‘junk cell’ tester. It’s now ~ 450mA with very little use. That’s worse than a AAA cell.
There’s a whole world of cool stuff out there at pretty reasonable cost if you do a little homework. It’s worth the time and effort.