Battery Characteristics

I remember reading an article about batteries some where (maybe here or else where), but this characteristic some batteries have, and I dont know what its called. But they exbit the following effect, (from memory) "When batteries seem like they are dead, they actually have some charge in them that will only last for a short period" Ie, A Dead 1.5V will be seen as .9V or lower, however, it can still supply 1.5V for a short period of time.

What is this called? Ive noticed that my Boost converter Will start up even though when I measure battery voltage, my meters reads .620V! The IC itself requires .9V to start up, but can stay operational down to .7V,

It's roughly comparable to dielectric absorption in a capacitor. I'd call it surface charge but that's something that occurs on peak charged batteries rather than dead ones.