I am no expert in this area, but I would have thought the electricity savings were nil, after all you have to use electricity to recharge the battery afterwards, which will use more electricity than you saved.
I would have thought you will save FAR more energy worrying about the heating, cooling and lighting. All these use a lot of electricity.
I found a web site where this qustion about laptops was asked,
Q. My laptop computer runs for five hours on a charge. Does it take more electricity to recharge the battery when it's dead than it would have taken to run the computer off the power adapter for those five hours instead?
A. Yes, a little bit, because transferring energy from one source to another is always less than 100% efficient. But the difference is not significant. It's not worth measuring.
This site below may be useful (it is where I got the laptop question from)
http://michaelbluejay.com/electricity/