
Why do we use so many units for energy? - IvanK_net
http://imgur.com/a/4L2d5
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al2o3cr
Short short answer: because those voltages are "nominal", not what's really
observed in-circuit. The available output charge (ampere*time -> charge) is
much more controllable during manufacture, as it's directly related to the
quantity of available reactants within the battery.

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gus_massa
You forgot to add the heat units, like BTU and calories, and the units for
food like "kalories", and the units for air conditioners, like "frigorie".

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IvanK_net
You are right, it is even more complicated, than the picture says.

