My laptop has a lithium ion battery, which has served me well for a year or so. Lasting rougly 3 hours at 100%. But a few days ago, when my battery was removed from the laptop for half an hour or so, the capactiy dropped to 15 minutes. 

I know how these batteries "wear down" over time, due to corrotion of the lithium cathode and whatnot. But I would've expected a steady decline, rather than a sudden and extreme fall in capacity. 

Actual question: Why did the capacity of my lithium-ion battery suddenly drop from 3 hours to 15 minutes? And was it related to the fact that the battery was removed from the laptop.

On a number of brush metal laptops/appliances if you run your finger lightly across the surface it creates a vibration sensation in your fingertip; this is not friction it is an actual vibration, I can categorically say that it is caused by some kind of electrical interaction is that the sensation only happens when your appliance is plugged into the AC power which suggest it is something to do with the frequency of AC power, but my question relates to the actual interaction between the metal surface and my finger, what is causing the feeling?