Lots of MoBo's use 2032 coin batteries. I've got a couple of boxes of 'em (don't ask!) well in date. Pm me and I'll send you one if you like. Well worth giving the holder a bit of a poke to tighten it up while you are doing the change... hopefully you won't have to get the soldering iron out this time.
Don't worry about losing your settings: looks as tho' you already have done so, & that's why the BIOS doesn't recognise your graphics card any longer. Just hit <del> when booting up and reset all to your liking.
Usual dire warnings about earthing yourself & using non-metallic pokey things apply of course.