First Generation Ampera and Volt
As quite a few people seem to be doing this, I thought I'd post the details.
1) Unlock car, switch off. Remove floor panel in boot. 4 nuts, M10 I think, 1 in each corner.
2) Undo & remove the -ve cable.
3) Remove the vent pipe.
4) Unclip (2 tabs I think) the large plastic fuse-box thing on top...