Well, I bought a GX680 II and didnt quite do my research. Now I am looking for a battery pack for the camera that takes AA batteries. I prefer the pack that is made for the II but I would also be interested in the packs for the III too.
I did the same and replaced the original battery which had died and got the AA battery holder. Depending on the model of 680 you have, you may need to doctor the battery holder to make it work. Mine involved drilling a small hole in the back of the holder so that one of the prongs behind where the original battery was could poke out. This meant the difference between the camera firing up and not working at all.