In my original posting on problem charging, I had focused on the 8000 series. Recently however, I found this blog post on the same issue of the mice not charging but it appears this issue is in the 7000 as well as and 8000 series mice. It appears Peter’s mouse, a 7000 series, doesn’t have a sensor as mine did, but it still doesn’t charge. I’m just going to repost my comment on his page, since it pretty much sums up everything:
I have also posted about this issue in the 8000 series mice. I’m not sure if your situation is specific to the 7000 series or if there was a hardware update, but there is definitely a switch in the 8000 series mouse I fixed. I might guess that they did an update to remove the completely superfluous sensor, but didn’t account for this additional problem in the revised design.
I hope it’s simply a different design, because if it was an update, it was again not well tested.