I just committed an inadvertent blunder that I thought I'd share in case it might help others.
I ordered a couple of 18650 Lithium Ion batteries for a robot vehicle that I'm building. I saw that these batteries were "protected" at the point that I ordered them, but did not consider the implication - after all an 18650 has a standard dimension as the name suggests, right? Well, it turns out that the protection circuit increases the length of the battery - in this instance by slightly more than 3 mm and I'd probably have to destroy the battery holder to get them to fit. Oh well, I can probably use these in a flashlight 
. I'll need to order new unprotected ones for the robot. I'm a little surprised that the clips in the battery holder don't give a little more.
