Q: I just bought a new battery for my MacBook but when I click on the battery icon it is says no battery available. Why?

Hi....

Try restarting your Mac ...

"Keep in mind that once the new battery is inserted, you will need to press the power button to start up the computer."

From here > MacBook Pro: How to remove or install the battery

If it restarts ok the battery icon should be available from the status menu bar.