New battery seems dead, won't charge

Followed this guide, which seemed straightforward. Once the replacement battery was in (which I purchased from this website) the battery would not charge. Computer starts up and runs fine with charger plugged in, but as soon as charger is disconnected it shuts off. I then reset the SMC and PRAM, but still nothing. I double-checked the connection from the battery to the I/O board. Anyone have any ideas? Did I get a dud?