Q: When I turn my keyboard on, the green light comes on for a few seconds and then turns off. The batteries are brand new. How do I fix this?

The green light indicated the keyboard has power, it will not stay illuminated. Therefore your keyboard appears to be working perfectly.

You did not indicate that in your first post. Please click Troubleshooting wireless mouse and keyboard issues - Apple Support and follow each step until the solution is found.

Use a USB keyboard, if you don't have one then either borrow or buy one. They are inexpensive. It isn't a bad idea to always have one on-hand in the event of future wireless keyboard problems. Once you have the USB keyboard then begin the troubleshooting.

Not a horrible idea.