At an electrolyte temperature above 30°C, the correction value is added to the actual reading of the hydrometer. If the electrolyte temperature is below 20°C, then the correction value is subtracted accordingly. When the electrolyte temperature is in the range of 20–30°C, no temperature correction is applied.
After determining the density of the electrolyte in each cell of the battery, the degree of its discharge is established according to the table Electrolyte density at 25°C, g / cm3. A battery discharged by more than 25% in winter and more than 50% in summer should be removed from the vehicle and recharged.
When measuring density, be careful not to drop drops of electrolyte containing sulfuric acid on the surface of the battery, body and other parts from the pipette, which causes corrosion, current leakage, etc.
To avoid incorrect results, do not measure the density of the electrolyte:
- if its level does not correspond to the norm;
- if the electrolyte is too hot or cold; optimum temperature when measuring density 15–27°С;
- after adding distilled water. You should wait until the electrolyte is mixed; if the battery is low, this may even take several hours;
- after a few starts. It is necessary to wait for a uniform density of the electrolyte in the battery cell to be established;
- at «boiling» electrolyte. You should wait until the bubbles in the electrolyte collected in the hydrometer pipette rise to the surface.
Temperature correction to hydrometer readings when measuring electrolyte density
Electrolyte temperature,°С | Correction, g/cm3 |
-40 to -26 | -0,04 |
from -25 to -11 | -0,03 |
-10 to +4 | -0,02 |
from +5 to +19 | -0,01 |
from +20 to +30 | 0,00 |
from +31 to +45 | +0,01 |
Electrolyte density at 25°С, g/cm3
climatic region (average monthly air temperature in January,°С) | Season | Fully charged battery | Battery low | |
by 25% | by 50% | |||
Very cold (-50 to -30) | Winter | 1,30 | 1,26 | 1,22 |
Summer | 1,28 | 1,24 | 1,20 | |
Cold (from -30 to -15) | All year round | 1,28 | 1,24 | 1,20 |
Moderate (-15 to -8) | All year round | 1,28 | 1,24 | 1,20 |
warm humid (from 0 to +4) | All year round | 1,23 | 1,19 | 1,15 |
hot dry (-15 to +4) | All year round | 1,23 | 1,19 | 1,15 |