Automobile Engineering in ME
The main characteristics of a maintenance free (MF) battery is that

Recharging of a maintenance free battery is neither required nor possible
A maintenance free battery has a relatively short shelf life when compared with standard batteries
A maintenance free battery requires little maintenance during normal use and it is sufficient to add water instead of an electrolyte containing sulphuric acid
Since it is sealed, the water in maintenance free battery is not lost through evaporation thus accordingly it is not necessary to top up the cells with water

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