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A United States Navy Aviation boatswain's mate tests the specific gravity of JP-5 fuel. Relative density, also called specific gravity, [1] [2] is a dimensionless quantity defined as the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material.
A hydrometer can be used to test the specific gravity of each cell as a measure of its state of charge. Because the electrolyte takes part in the charge-discharge reaction, this battery has one major advantage over other chemistries: it is relatively simple to determine the state of charge by merely measuring the specific gravity of the ...
In some types of battery, electrolyte specific gravity may be related to state of charge but this is not measurable on typical battery pack cells, and is not related to state of charge on most battery types. Most SOC methods take into account voltage and current as well as temperature and other aspects of the discharge and charge process to in ...
Pendulum clock driven by three weights as "gravity battery". An old and simple application is the pendulum clock driven by a weight, which at 1 kg and 1 m travel can store nearly 10 Newton-meter [Nm], Joule [J] or Watt-second [Ws], thus 1/3600 of a Watt-hour [Wh], while a typical Lithium-ion battery 18650 cell [2] can hold about 7 Wh, thus 2500 times more at 1/20 of the weight.
Specific energy Energy density (W⋅h/L) Comment Zinc-air battery: 1.59 [48] 6.02 441.7 1 672.2: controlled electric discharge Lithium air battery (rechargeable) 9.0 [49] 2,500.0 controlled electric discharge Sodium sulfur battery: 0.54–0.86 150–240 Lithium metal battery: 1.8 4.32 500 1200: controlled electric discharge Lithium-ion battery
The state of charge of a lead-acid battery can be estimated from the density of the sulfuric acid solution used as electrolyte. A hydrometer calibrated to read specific gravity relative to water at 60 °F (16 °C) is a standard tool for servicing automobile batteries. Tables are used to correct the reading to the standard temperature.
To find SoC from specific gravity, a look-up table of SG vs SoC is needed. Refractometry has been shown to be a viable method for continuous monitoring of the state of charge. The refractive index of the battery electrolyte is directly relatable to the specific gravity or density of the electrolyte of the cell. [13] [14]
Electric charge is a conserved property: the net charge of an isolated system, the quantity of positive charge minus the amount of negative charge, cannot change. Electric charge is carried by subatomic particles. In ordinary matter, negative charge is carried by electrons, and positive charge is carried by the protons in the nuclei of atoms ...