Abstract: A method and device for filling a container with liquid up to a predetermined level. The device includes a cylinder and a piston movable within the cylinder between a rest position and a fill position. A supply of liquid for filling the container is provided to a first end of the piston at alternating pressures to cycle the piston back and forth between the rest and fill positions. Each time the piston reaches its fill position, supply liquid is added to the container. With each cycle the device draws fluid from the container and then attempts to compress the drawn fluid with a second end of the piston. When the fluid drawn is gas, the piston can compress the gas to continue moving to the fill position. When the drawn fluid is liquid, the piston can not compress the liquid and thus is stopped to prevent further filling.

Abstract: An electrolyte level monitor used in combination with a battery having multiple cells. The monitor includes a circuit having an indicator which operates when the electrolyte level is at or above the minimum acceptable electrolyte level. The circuit is connected across cells of the battery to provide a potential to operate the monitor.