It seems like I have recurring problems with alkaline batteries leaking. I had a streamlight LED that took 3 AAAA and I noticed at one point that it wouldn't turn off completely. I inspected the batteries and found that they had leaked. Since that was a rarely used light I figured it was just a bad idea to let the batteries sit in the lights. I took the batteries out of all but the two lights I use regularly.
Recently with another streamlight (7 LED 4 AA model)--one of the two regular users--I used the light and it seemed decently bright, and then I noticed that it wasn't turning all the way off. And sure enough, the batteries had leaked.
Why are these batteries leaking? I recall hearing that alkalines might be subject to leaking if they get overdrained, but these batteries were stilling giving decent light output.