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

A maintenance free battery requires little maintenance during normal use and it is sufficient to add water instead of an electrolyte containing sulphuric acid
A maintenance free battery has a relatively short shelf life when compared with standard batteries
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
Recharging of a maintenance free battery is neither required nor possible

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Automobile Engineering in ME
The function of positive crankcase ventilation (PCV) system is that it

Feeds blow by gases to the exhaust manifold
Returns blow by gases from the crankcase to the intake system
Mixes fuel with air
Promotes combustion by creating a swirling movement in the air-fuel mixture

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