You're right that it doesn't make any sense to talk about it without defining it, but I'd say that consciousness is based on your brain having access to parts of itself internally, not just the outside word, and that bats presumably do have it.

I find that people who complain about "defining" consciousness are, in fact, Mysterians who opposed the very idea of such a definition.

All we need to do (to talk about, to study it) is identify it. We need to be using the word to refer to the same thing. And there's nothing really hard about that.