Specific Gravity Of Electrolyte

WARNING: This page is about a different variant/trim than selected.

Check the specific gravity of the electrolyte using a hydrometer and a thermometer.

NOTE:

Specific gravity varies with temperature of electrolyte so that it must be corrected at 20°C (68°F) using the following calculation:

S20 = St + 0.0007 x (t - 20)

S20: Specific gravity corrected at electrolyte temperature of 20°C

St: Measured specific gravity

t: Measured temperature (°C)

When measuring in a simplified manner using the battery terminal voltage, calculate the specific gravity by the following formula.

Specific gravity = [0.187 x battery terminal voltage (V)] - 1.1

Perform the steps 1) and 2) before measuring the voltage in order to stabilize the voltage.

Turn the ignition switch to OFF and illuminate the headlight for 30 seconds.
After turning off the headlight, leave the vehicle for one minute.
- Measuring the specific gravity of the electrolyte in the battery will disclose the state of charge of the battery. The relation between specific gravity and state of charge is as shown in the figure.

Fig 1: Specific Gravity And State Of Charge Graph

Courtesy of SUBARU OF AMERICA, INC.

Fig 2: Specific Gravity And Electrolyte Temperature Graph

Courtesy of SUBARU OF AMERICA, INC.

Check

Specific gravity: 1.250 - 1.290, and difference between cells is 0.04 or less → Battery is normal
Specific gravity: Less than 1.250, or difference between cells is 0.04 or more → Battery needs to be charged or replaced