Thanks for you reply. I thought my early 2011 macbook pro has a removable battery. But the link below seems to suggest otherwise. How do I confirm if my mac has a removable battery?
https://support.apple.com/en-us/HT204054
"Servicing the battery in your Mac notebook
MacBook, MacBook Air, and MacBook Pro computers with built-in batteries should only have their batteries replaced by an Apple Authorized Service Provider or Apple Retail Store. Attempting to replace a built-in battery yourself could damage your equipment, and such damage is not covered by warranty.
These Mac notebooks have built-in batteries:
- MacBook (13-inch, Late 2009) and later
- MacBook (Retina, 12-inch, Early 2015) and later
- All MacBook Air computers
- All MacBook Pro computers with Retina display
- MacBook Pro (13-inch, Mid 2009) and later; MacBook Pro (15-inch, Mid 2009) and later
Most older Mac notebooks have removable batteries that you can replace yourself. Contact an Apple Authorized Service Provider or Apple Retail Store for assistance servicing a removable battery."