Gastight Sealed (secondary) Cell
A secondary cell which remains closed and does not release either gas or liquid when operated within the limits and temperature specified by the manufacturer. The cell may be equipped with a safety device to prevent dangerously high internal pressure. The cell does not require addition to the electrolyte and is designed to operate during its life in its original sealed state.
Source: IEC 61892-6, Mobile and fixed offshore units – Electrical installations – Part 6: Installation. Global Standards