Abstract: An air-vented battery cell containing liquid electrolyte is rendered leakproof against spillage during shipping and during usages when the cell is tilted from a vertical position in any direction to a horizontal position, as when used on a marine buoy, by providing the cell with a vent reservoir across the top thereof having a liquid connection with the cell at only one corner thereof and having a vent tube in the reservoir at the top part thereof, leading through one end wall diagonally to nearly an opposite corner portion thereof. In three tilt positions of this cell at 90.degree.