MacBook Pro 15 – is my battery dead?

(note, this is a macbook pro, 15 in)
ok, so i reach for my computer, and its dead. i could have sworn i only closed the lid. i plugged it in thinking that this was probably just a dead battery, but this is turning out to be far worse.

after booting back up, with the charger in, the little battery icon on the task bar has an 'x' over it. if i unplug the computer, it turns off. its obviously not retaining power in the battery, but what confuses me is why. it was working fine just last night.

ive tried googling the problem, and the only thing ive come up with so far is apple help articles. i did what they said and went through with resetting the smc, but have had no luck.

if anyone could possibly shed some light on the problem, i would greatly appreciate it.