I've been wondering how to avoid taking the batteries out to check water level. Some wooden stir sticks or tongue depressors with a clip-on stop to limit the length could be dipped into cells like a dipstick. A bit of measuring and testing could create a table listing the amount of water needed to top up a cell with any starting level. Then the correct amount of water could be added to a cell with a syringe having a short curved tube on the business end while the battery is in place in its compartment.