The test is carried out with a density meter. When determining the density of the electrolyte, it is necessary to take into account the battery temperature. If the electrolyte temperature is below 15°C, for every 10° below this temperature, subtract 0.007 from the measured density. For every 10° above 15°, add 0.007.
The density of the electrolyte in the battery must be within the following limits:
| Temperature | Above 25°C | Below 25°C |
| Full charge | 1,210 – 1,230 | 1,270 – 1,290 |
| Charging 70% | 1,170 – 1,190 | 1,230 – 1,250 |
| Discharged | 1,050 – 1,070 | 1,110 – 1,130 |
Measure the specific gravity of the electrolyte in each can. A difference in specific gravity of 0.04 or more between any two cans indicates electrolyte loss or sulfation of the plates.
If the electrolyte density between any two cans differs by more than 0.04, the battery must be replaced. If the electrolyte density is lower than required, but the same in all cans, the battery must be charged.
In case of using a maintenance-free battery, the battery condition can only be checked with a voltmeter. In batteries with a built-in charge level indicator, the battery condition is determined by the color of the indicator. The green color of the indicator corresponds to a full charge of the battery. The black color of the indicator indicates the need to charge the battery. The blue color of the indicator indicates a low electrolyte level in the battery.
(Information copied from the website: MercedesMan.ru)