Considering a 4-cell (laptop) lithium-ion battery, the cell voltages add (since they are in series) to 3.7 V * 4 = 14.8 V. However, the adapter says that it has a 19.5 V DC output. I want to know why is it 19.5 V and not some other value like 14.8 V itself or 24 V for instance?
Also, my adapter says Input: 100-240 V ~ 1.6 A and Output: 19.5 V - 3.33 A (65 W). Does it mean that the adapter efficiency is 65 W/(1.6 A*230V) assuming that the mains voltage is 230 V? Am I actually paying bills for 230*1.6 W or is it that 1.6 A is the maximum current that can be drawn and the actual current varies?