Why are Watt Hours not Watts per Hour? Are they the same thing?
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Imagine machines that pump water. You might want to compare these to each other by the amount of water they can pump. So you invent a new unit for pumped gallons per minute, you call it a galmin. A machine with two galmins is twice as powerful as a machine with one galmin. But later you might want to know how much water the machine pumped in an hour, so you calculate 2 galmins * 60 minutes = 120 galminminutes. This is redundant, but all manuals are written with galmins in mind, laws already exist and whole industries only work with galmins, so instead of using gallons, you use galminminutes, even though those mean the same.
This might seem stupid, but it is what happened when steam engines became popular. People wanted to compare engines and so invented a unit to measure their power: the Watt. Only later did they want to calculate the energy, that “flows” through the engine. It took mankind some time to understand, that this “energy” was a real thing. Nowadays we think of energy as a real thing, we understand that for example a full battery is full of energy and an empty one is not. But we already build everything around Watt as the unit for power, now we hat to define energy as Watt * hours an engine is running = Watt Hours.
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