I know this is said to be true for cellphones, electric shavers, and digital cameras, etc. You shouldn't charge them when not necessary and unplug them when the charge is done so that the battery lasts longer over its lifetime.
I just wanted to check if this applies to all batter-powered household items like those mini-vacuums. I guess I can't think of many other examples right now. Such things tend to have a "dock" and people automatically put it into them which makes them charge whenever it's not in use. And silly question part two does this hurt the battery/energy performance when it IS in use, in addition to reducing the lifetime?