1) Battery shape 2) Common toy go-with 3) Largish cell 4) Many a toy powerer 5) Power source for a toy, often 6) Toy car driver 
The `C` battery (or R14 battery) is a standard size of battery typically used in medium-drain applications such as toys and musical instruments. As of 2007, C batteries accounted for 4% of alkaline primary battery sales in the United States. In Switzerland as of 2008, C batteries totalled 5.4% of primary battery sales and 3.4% of secondary batte.....
[n] - battery used to maintain the grid potential in a vacuum tube
noun battery used to maintain the grid potential in a vacuum tube