Hi Morky,
What device do you want to use your white LEDs in? A torch?
One white LED isn't bright enough for a torch. maybe just a keyring one up close. You will need to use a bunch of LEDs, each with its own current-limiting resistor.
As said by Jim, a little 9V battery doesn't have much power. Inside are six AAAA cells. Those cells are very slim and tiny. Tiny cells are very expensive when compared to common larger cells like AA size that have nearly 5 times the capacity.
There is a project that maybe is too advanced for you right now, but it explains the problems of little 9V batteries and compares them with larger cells. The project is an electronic circuit that boosts the voltage of two larger cells to 9V. If you go to the publisher's web-site, they want you to pay to see their project. However, if you go to
www.google.com and enter into the search bar, Silicon Chip Never Buy, then the 1st link is to the entire article for free.
The publisher is Silicon Chip magazine in Australia, and the project is Never Buy a 9V Battery Again. Google's links are interesting, Never Buy a Dell Computer, Never Buy a Rusty Ford, etc. :lol: