Nickel-cadmium battery vented cell type
Overview
 
Vented cell is a type of nickel–cadmium battery that is used when large capacities and high discharge rates are required. The term vented refers to a difference to common NiCd batteries which are sealed.

They are used in aviation, rail and mass transit, backup power for telecoms, engine starting for backup turbines etc. Using vented cell NiCd batteries results in reduction in size, weight and maintenance requirements over other types of batteries.
 
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