The watt-hour per kilogram (
SI symbol: W⋅h/kg) is a unit of
specific energy
Specific energy or massic energy is energy per unit mass. It is also sometimes called gravimetric energy density, which is not to be confused with energy density, which is defined as energy per unit volume. It is used to quantify, for example, sto ...
commonly used to measure the density of
energy
In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of hea ...
in
batteries and
capacitor
A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals.
The effect of ...
s.
SI Units
In the
SI system of measurement, one watt-hour per kilogram is equal to 3600
joules
The joule ( , ; symbol: J) is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applied. ...
per kilogram.
Typical values
The batteries that
Tesla uses in their electric cars deliver about 254 W⋅h/kg, compared to
supercapacitors that are typically rated between 3–10 W⋅h/kg, with the best commercially available supercapacitors as high as 47 W⋅h/kg.
Nuclear batteries based on
betavoltaics
A betavoltaic device (betavoltaic cell or betavoltaic battery) is a type of nuclear battery which generates electric current from beta particles (electrons) emitted from a radioactive source, using semiconductor junctions. A common source used is ...
can reach up to 3300 W⋅h/kg, although over much longer time periods.
Prototype Nuclear Battery
phys.org, June 6 2018
References
Units of energy
Mass
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