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HOMESERVICE MANUALSVOLVO2009C70 AUTOMATICREPAIR AND DIAGNOSISACCESSORIES & EQUIPMENTGAUGES & INSTRUMENT PANELSELECTRONICS - DESIGN AND FUNCTION - 1 OF 4BATTERYDESIGN AND FUNCTIONACID DENSITY
2009 Volvo C70 Automatic

Acid Density

2009 Volvo C70 AutomaticSECTION Acid Density
Fig 1: Battery Acid Density
GLL102559Courtesy of VOLVO CARS CORPORATION

Example of the variation in the stand-by voltage and in the density of the acid with the state of charge in a battery (of open type) at +25°C (77°F) (measured after approx. 2 hours charging or discharging) 

  1. A. Stand-by voltage in V
  2. B. Acid density in g/cm3
  3. C. State of charge, SOC, in %
  4. D. Variation in the stand-by voltage with the state of charge
  5. E. Variation in the density of the acid with the state of charge.

The density of the acid is a unit showing the concentration of sulfuric acid in the electrolyte. The density of the acid is a measurement of the battery voltage and STATE OF CHARGE, SOC . The density of the acid is measured in g/cm3 . Sulfuric acid is required for the chemical processes in the battery.

The higher the value of the acid (i. e. high concentration of sulfuric acid), the higher the voltage and state of charge. A low acid density value means a correspondingly low concentration of sulfuric acid, low voltage and a reduced capability for providing current. The electrolyte in a fully charged battery has a density of 1.28 g/cm3 at +25°C (+77°F). The density of the electrolyte in a fully discharged battery is 1.10 g/cm3 or lower depending on the type of battery.

The illustration shows how the stand-by voltage and the density of the acid drops as the state of charge of a battery reduces.

HINT: For maintenance-free as well as sealed batteries (AGM) the battery acid cannot be accessed and thus its density cannot be measured. 

RENDER: 1.0x

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