MacBook, MacBook Pro, MacBook Air: Battery not recognized after being fully drained
If the battery in your MacBook, MacBook Air, or MacBook Pro is fully drained of power, the battery will put itself into a low power state to preserve its ability to charge in the future. Fully draining the battery can be done by running the battery until the computer sleeps and then leaving the battery in the sleeping computer for several months or more without plugging it in.
Once you have fully drained the battery, when you plug in the MacBook, MacBook Air, or MacBook Pro's power cord and start the computer up, you may see an X over the battery icon in the menu bar. If you see this, allow the battery up to five minutes to come out of its low power mode and begin accepting a charge again. If your battery still is not recognized by the computer—if it still has an X over the icon—after five minutes, you may want to reseat the battery on your MacBook or MacBook Pro (applicable only to models with removable batteries). If the battery still isn't recognized after reseating, try resetting the SMC. If the battery is not recognized after those steps please contact AppleCare for further assistance.