Why CMOS battery doen't keep settings?

If you are sure that your CMOS  battery is good, but the setting are always reset to default after shutdown,
try this;
After shutdown yor computer,
1.remove your battery from the socket.
2. you will see the negative contact point
3. clean the contact point with contact cleaner or very fine amery paper to get shining
4. If you are using amery paper be sure that remove particles are wiped away from the motherboard surface.
5. To get proper contact with the battery slightly bend the contact plate upward with a suitable tool.
6. Repeat the step 3 to the positive contact point also.
7. Replace the battery and start the computer.
8. change your settings of SETUP eg. Time and Date and save.

Im sure this will be the last change........