I got an iPad 8 gen iPad this December. After a few months the battery life started working only 4 and half to 5 hours. The battery life is supposed to last for about 10 hours.

Start here:

If your iPad won't charge – Apple Support

Charge and monitor the iPad battery - Apple Support

As described your battery may be defective or require replacement. Assuming that the iPad remains functional, you would be well advised to directly contact Apple Support - and request a remote battery test. The result of the test may better inform your next steps.

You will find the Get Support link at top-right of this page. Alternatively, you can open a support case using the excellent Apple Support App. If not already installed on your iPad, the App can be downloaded from the App Store:

https://apps.apple.com/gb/app/apple-support/id1130498044

As a further alternative, you might visit the Genius Bar at your local Apple Store - where the technicians will be able to test and assess you iPad.