When testing a battery, it is not just the charge state and load which must be checked. The charger or alternator should also be checked because charging the battery incorrectly affects the reliability and load of the battery.
The charge state of the battery is measured with a voltmeter. This should take place between 1 to 2 hours after the battery is charged or discharged. It measures the quiescent voltage and the terminal voltage:
U0 = (acid density + 0,84) x n
n= number of cells (n = 6 for a 12V-battery)
If the quiescent voltage is 12.24 V then the quiescent voltage per cell is:
12,24 V / 6 = 2,04
Acid density = 2,04-0,84 = 1,20
|100% charged battery||12,75 V|
|Empty battery||11,75 V|
Measuring the concentration is only possible for batteries with screw plugs, e.g. the Sepahan standard battery.
The concentration of the sulfuric acid in the battery fluid decreases as the battery discharges. The concentration measured as a specific mass (kg/m³) is a useful measurement for identifying the charge state of a battery.
The concentration is measured with a (m) hydrometer with the appropriate scale marked on it:
|100% charged battery||1,28 kg/l at 25°C|
|50% charged battery||1,18 kg/l at 25°C|