Started getting a few Apple Mac’s coming in for repair with battery problems.
If an X appears on the battery icon in the menu bar
Your battery may not be installed properly or your computer may not recognize it
If the battery icon in the menu bar contains an X, either your Mac does not recognize the battery or the battery is not properly installed in your portable Mac.
If a battery is fully charged, but you still see an X: Your Mac may not recognize the battery. After you plug in your Mac and let the battery charge for five minutes, the battery should be recognized.
Your battery can become fully drained if you use your Mac unplugged until it puts itself to sleep or if you leave it in sleep mode for an extended period.
If your computer has an accessible battery: If you can access the battery, remove it, then reinstall it. Refer to the manual that came with your Mac for more information about properly installing the battery
If an X appears on the battery icon in the menu bar your battery may not be installed properly or your computer may not recognise it