Where do I find on the motherboard, the battery for the Advent netbook

Since you did not include the model number of the netbook, I will give you a couple of generic locations where you may find the CMOS battery.
It could be tucked away under the keyboard encased in yellow plastic; or on some models, you would find it by removing the battery pack; remove the large cover over the cooling fan; in the upper left corner is a white oblong cover with two screws- remove that piece and the CMOS battery should be held in place with tape.