It's actually bad to keep it continuously plugged in, I've heard...
I've heard it's actually bad to keep a lithium ion permanently plugged in. The battery actually needs occasional charge and discharge.
I have seen evidence this is true based off of laptop batteries when it comes to recycling time... I have 2 users who have laptops but couldn't tell you how to undock them without a call to support. (OK actually they both just retired in the last two months). When it came time to recycling our Dell D620s and D630s, without fail every person whose laptop was always on the dock had a non-functional battery. Every single one. Those who used it as a normal notebook system had functional batteries, for the most part. Out of say a sampling of 50 or so I'm talking here, so not huge but still noticeable.
Also, I've also heard operating a battery operated device that normally works on battery without a battery in it will potentially cause issue on "some" systems. The issue here is the battery itself acts as a capacitor. Power variances are absorbed into the battery, not the device. I don't know if the operating system of some devices would recover a quick or minor hardware issue better than others, so this may or may not be noticeable to the end user. But even so, you may still have things happening in the back end. I've heard this specifically w/ wireless Crestron panels which is just a small tablet w/ WinXP embedded in it when it comes down to it.
