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

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
A maintenance free battery requires little maintenance during normal use and it is sufficient to add water instead of an electrolyte containing sulphuric acid
Recharging of a maintenance free battery is neither required nor possible

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Automobile Engineering in ME
The main function of the tread pattern on tyre is that

The crests between the tread grooves absorb road noise
In wet conditions, the tread grooves expel water that is drawn between the tyre and road surface
The tread grooves pass air between the tyre and road surface, thereby preventing tyre from overheating
The tread pattern protects the tyre's inner carcass from small stones and pieces of glass

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