My battery gave a failed signal for a while, and then it began working again. This happened after the first cycle. MagSafe2 stayed completely green--rather than going to amber; a reboot and replug caused it to fix itself -- it will probably happen again, unfortunately...
The 13 inch's tab is a bit more difficult to reinstall than uninstall. Delicate care is needed.
While reversing the guide and installing the battery the plastic connector was frustratingly hard to connect to the logic board, but the guide is good in itself. It took me about 25-30 minutes, but I am finicky and overly careful. If your laptop is especially old, I would suggest having a can of air on hand.