Did a bunch of research, and this Deka ETx14 Battery is a winner! Not the very bestest battery possible, as that title seems to go to the Antigravity battery, but at <$70 vs ~$220, this Deka got my active vote.
and.. it's made in the USA.

fwiw- this is (I hope) the correct sizing for the F800GS, according to folks on ADVRider, altho Deka did not list anything for the F8 at all.