I find it convenient to just leave the charger sitting on my desk, still plugged into the wall, so that I can just pop the battery in when I need it, but I wonder if this is bad for the charger in the long term?
It doesn't appear to be doing anything without the battery in place, and it doesn't feel warm, but could there be any damage or even safety issues to consider?
I realize this may not be considered on-topic for Photo.SE, but I am interested in this specifically for my Nikon MH-18a charger and my EN-EL3e battery for my Nikon D90, though I suspect (hope?) that this will be of general interest to owners of other gear.
If you want to vote to close this question, I'm OK with that too.