Q: my Macbook air losing charge faster than normal

Try these steps: Resetting the System Management Controller (SMC) on your Mac - Apple Support

If this does not help, I'd suggest to use the safe mode boot:

Shut down your Mac

- Wait until your computer turns off and after that press the Power button

- Right after you hear the startup tone, press and hold the Shift key

- Release the Shift key when you see a grey Apple sign and the progress bar below this sign

- Once you see Desktop, start a Disk Utility scan to detect and repair file system errors (don't forget to choose your main hard drive)

- Click on Verify Disc and then, if asked to fix problems, on Repair Disk

- After this, click on Verify Disk Permissions and then on Repair Disk Permissions

- After the process is finished, shut down your Mac and turn it back on after about 30 seconds

If this does not help, I believe you need to contact Apple Support: https://www.apple.com/support/macbook/contact/

What is 'normal' and what is 'faster than normal'?  What applications do you have open?

https://support.apple.com/en-us/HT203184

Ciao.