So this is not so much as a workshop tool, more like a workshop tip. I got fed up with having trouble filling up my battery to the correct mark using a funnel. It was too easy to over fill it.
Now what I do is I have a bottle of battery water with a tight fitting tube through the top to the bottom of the bottle. That way I just need to place the other end of the tube in the battery cell and squeeze the bottle to deliver the water till it gets to the max level and then just stop squeezing and it stops immediately. But maybe you guys already do this!