Someone on here probably has much better ideas...but I was trying to find something I could use to top off battery water levels....in those hard to reach places. Funnels don't always fit, they blind you so that you can't tell when it's getting full and overflow, etc, etc.
So....I was looking for something that would work for that application and ran across cheap mustard and ketchup plastic bottles with a nice needle nose and cap. Unscrew the lid, fill with DI water, and fill the battery cells - even in tight places.