Is there any mechanism or tweak to keep the passwords permanently for BIOS?
If I remove the CMOS battery for a while, the password gets reset. How can I prevent this?
You can't. When you remove the CMOS battery, the chip which stores the password (and other BIOS configuration) loses power and eventually forgets the stored configuration.
If you want to password-protect the BIOS and avoid people removing the CMOS battery to reset it, you should look into physical security for the computer case.