Check the density of the electrolyte in the battery every 3 months.
Check with a hydrometer. When determining the density of an electrolyte, its temperature must be taken into account. For electrolyte temperatures below 15°C, for every 10°C below this temperature, subtract 0.007 from the measured density; over 15°C add 0.007.
After determining the density of the electrolyte in each battery bank, set the degree of its discharge according to Table. 9.1.
Measure the density of the electrolyte in each jar. Density difference 0.04 g/cm3 or more between any two banks indicates electrolyte loss or plate sulfation.
If the density of the electrolyte between any two banks differs by more than 0.04 g/cm3, replace the battery. If the electrolyte density is lower than required, but the same in all banks, charge the battery.
The performance of a maintenance-free battery can only be checked with a voltmeter. The state of charge of the battery with a built-in indicator is determined by the color of the indicator. The green color of the indicator corresponds to a full charge, black indicates the need for charging, blue indicates a low level of electrolyte in the battery.