Recently I had the fun of replacing the CMOS Battery in an Asus EEE laptop. The old battery was a lot smaller than the new one. I drew a circle around the old CMOS battery so you can locate it.
The new one is bigger than the old one but there is room for it in front of where the old one was located. Totally disassembling of the laptop is not needed. For more instructions here is my old post on the subject: http://bobdavis321.blogspot.com/2010/12/asus-ee-disasembly.html
By the way I purchased the New CMOS battery for $3 on Ebay but now I cannot find one for less than $5?