How to switch mainboard battery?

Well I have two problems with my mainboard of nikon coolpix p7800

1. the battery that is at the top section is kind of fried.

Does any one know what kind of part this battery is?

and how to change it?(it's soldered at the mainboard)

This problem caused the camera to loose all the setings if you turn it off and on again.

the secound problem will be in the next question^^