Best I could find is the number for parts 800-999-4409. However, http://www.batteriesplus.com
or Radio Shack is where I purchase my CMOS batteries and they have extensive files.
The manual neglects to say "where" it is - My best "guess" is you will need to remove the large back cover and typically the CMOS battery is attached via a 2-lead pigtail.http://support.acer.com/acerpanam/Manuals/acer/2009/ServiceGuides/SG_AS4736_4736G_4736Z_4736ZG_4336_09152009.pdf
Good Luck! - Please post back.