Hey Ben Heck,
I'm currently building an electric bike battery pack out of used 18650 (laptop) cells, but I don't have a reliable way to test the capacity of each cell (to balance the pack)
there are capacity testing boards on ebay ($7-$hundreds) most only test one cell at a time...
I figure it would most likely use the arduino, to calculate and administer the test.
the testing current should be aprox 500ma/cell and it should stop after the battery reaches 3.0v
depending on which arduino you choose this could test 10+ cells at a time
Please let me know if you would like to tackle something like this.