Capacity (Wh) is the energy stored in the battery. Wh is Watt x hour.
Power (W) can be considered as the speed of drawing the energy. W is Watt.
Maximum Power (W) your battery allows to draw is indicated at the specifications of your battery. All devices you power from the battery together must not draw more than the limit.
For example,
Globalmediapro Li95S has Capacity of 95Wh and Max Power draw (Power limit) of 54W.
JVC GY-HM700 HD Camcorder draws 23W.
Comer CM-LED1800 LED Camera Light draws 20W.
You can use the Li95S battery to power the camera and light: 23W+20W=43W < 54W.
The 95Wh battery will last for approximately 95Wh / 43W = 2.2 hours.
To power the 43W system for 4 hours, you would need Capacity of 43W x 4 hours = 172Wh.
Related Category: Batteries and Power