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Maintainable. Only classic lead-acid batteries (see "Type") can be serviced: they are easy to distinguish even externally — by the presence of removable plugs that provide access to internal containers with electrolyte. The latter is a mixture of sulfuric acid with water, and with each charge, some of this water "boils away" (decomposes into oxygen and hydrogen and evaporates). This happens especially intensively during overcharging or charging at high voltage. Battery maintenance consists of periodically replenishing the water reserves in the electrolyte — without this, a decrease in its level leads to damage to the plates due to contact with air, which irreparably worsens the battery's characteristics. On average, maintenance should be carried out 1-2 times a year (15-20 thousand km of mileage for a passenger car) and these periods usually coincide with the terms of scheduled maintenance. However, this value may vary depending on the characteristics of both the battery itself and its operation; More detailed information is usually contained in the instructions for specific models. "Refilling" should be done exclusively with distilled water, since even a relatively small amount of foreign impurities can damage the plates.
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Maintenance free. As the name suggests, such batteries do not require the maintenance described above; this is achieved in a number of ways, in particular by filling the elect
...rolyte with a reserve for the entire service life or using gel (see "Type"). With obvious advantages due to ease of use, maintenance-free batteries at the same time have one drawback: they are much more sensitive to deep discharge (capacity decreases), and, accordingly, tolerate cold and long periods of downtime worse.
