Abstract: A battery filling system for use in efficiently adding water to, for example, those lead-acid batteries which are located in inconvenient or hard-to-reach places. The battery filling system includes a first flexible tube for use in transferring distilled water from the interior of a water-filled vessel to the hard-to-reach cell of a lead-acid battery. A second flexible tube transfers pressurized air from an external pressurized air source (typically human lungs) to the interior of the vessel in a quantity sufficient to cause the water to advance into and fill the first tube. A cap is used to snugly attach both tubes to the vessel. A means is also provided to minimize loss of air pressure from the vessel.