Well,

1/3 = .3333333333333333~
so 1/3 * 3 = .999999999999999~
So 1+1 does not equal quite 2 and therefore 2+2 doesn't quite equal 4.


other than that jdetray hit it right on the head. It's actually a good way to buy for 4 cell packs as you then have two 2 cells to use in smaller planes if you wish.