The CMOS battery is the RTC battery. (Real Time Clock Battery)
If memory serves it is under the Keyboard.
Same area as this NX7300,http://www.iarfhlaith.com/2008/08/23/how-to-repair-a-hp-nx7300-laptop/
Scroll the page down, look at the second to last photo.
(The one above the bold heading - The Final Test )
Click on the photo to enlarge.
(You can enlarge twice)
The red - Battery - points to the RTC battery.
Same holder, and style, as used on a Desktop PC motherboard.
Uses a CR2032 battery.
HP Compaq NX9110 Notebook PC - Service Manual,http://h20000.www2.hp.com/bizsupport/TechSupport/DocumentIndex.jsp?contentType=SupportManual&lang=en&cc=us&docIndexId=64179&taskId=135&prodTypeId=321957&prodSeriesId=395747
Under the bold subheading - Quick jump to manuals by category...
,click on the subheading - Service and maintenance information
Takes you down the page to the bold heading -
Service and maintenance information
Under this bold subheading there is just one file listed. (In blue)
Click on it.
HP Pavilion zx5000 Notebook PC, HP Pavilion zv5000 Notebook PC, Compaq Presario R3000 Notebook PC, HP Compaq NX9100 Notebook PC - Maintenance and Service Guide
This is a PDF file. The computer you are using now has Adobe Reader on it, which uses PDF files.
After you click on the above file name, it may take up to 30 seconds before the first page comes up.
For additional questions please post in a Comment.