How smart of you to ask, I just ordered both. Here was my thought with two short batteries you can use it both short or long. With the two long batteries you have a backup but it will only work as a long one unless you buy extra batteries. Since I thought the price was amazing and a back up is a good idea I got both. So I can have two long or two short or one of each and two spare batteries. I've heard the first version the longer 18560 rattled a bit, but with the v2 a better spring fixed it.