Calculate battery's Watt hours (Wh) and charging speed (W)

Calculate Battery's Watt hours

Wh=( mAh / 1000 ) × V

For example, battery with capacity of 4120mAh that operates at 10.8V has 44.50 Wh.

Wh = 4120 / 1000 * 10.8
Wh = 44.50

Watt = Volts x Amps

For example, device (when charging) reports 9V and 1.87Amp. The charging speed in Watts is:

Watts = 9 x 1.87 = 16.83