Following the unhappy end of my Nikon D3100, I have upgraded to a new D5200, as a result of which I now have an extra EN-EL14 Li-ion battery and MH-24 battery charger. It would be nice if I could save a little space in my camera bag by storing the extra battery in the slot designed for it in the charger. Is this safe? Will it deplete the battery's charge?
I have been storing my spare battery in the unplugged charger for the last 6 months and yes there was depletion of the charge ( 5% per month). I would have to do an experiment to find out if there was less depletion by storing it out of the charger. I never thought about whether it was safe or not until you asked the question. I have not had a problem with said battery being stored in the charger, but if you are worried, I would insert a piece of paper between the battery and the terminals on the charger. Just remember that li-ion batteries should never be completely depleted (never below 20%. For more info go here: http://arstechnica.com/gadgets/2011/02/ask-ars-what-is-the-best-way-to-use-an-li-ion-battery/ Also since you have now 2 li-ion batteries, you should rotate them to get the maximum life out of them. More info go here: http://www.kenrockwell.com/tech/battery-life.htm
An unplugged charger may, or may not, discharge the battery if it isn't plugged in to the wall. Depends entirely on the charger's circuitry and may change without notice, even if it's exactly the same model of charger (the model number guarantees it will charge the battery. It doesn't guarantee how it charges the battery)
However, if your battery is symmetrical just put it in the charger the other way round. I put my spare batteries in their chargers like this - takes up no extra space, and nothing is going to discharge itself if the contacts don't line up. The occasional charger has positioning lugs that get in the way, 10 seconds with the wire clippers takes care of that problem.
The problem here is that your battery is coming into contact with metal that will conduct electricity. So slight discharge will occur if metal is touching just one end of your battery. If its left on a battery charger its likely that the capacitors on the board of your charger will pull from your battery as well. That being said it should not damage the battery. Only drain them a bit.