They make one piece of plastic that has two sizes of holes. That way it will only mate one direction so you have less of a chance to plug in backwards.
Now the question i have for you is this, are both connectors the same size? They make a 3.5mm and a 4.0 mm, they look the same. I have the 3.5mm connectors so I have no idea how much difference there is between the 3.5 and 4mm.
The reason I ask is I was looking at the battery and it says it has a 4.0mm banana plug. So, if they are the same size yo are good to go.
http://www.hobbypartz.com/77p-sl2200-3s1p-20c-3333.html
Buzz.