Exactly, depending on the make/model that's either 3.0V, 2.8V or 2.5V lowest discharge limit. If you go under that you basically can not longer trust the cell integrity and should dispose of it (no matter what miracle workers on the web say, the copper in the cell will have gone into solution and it can be deposited anywhere at all, but never again in the same spot where it was supposed to be so you are essentially the proud owner of an incendiary with a random length fuse...).