I think the readers and some of the responders on this battery issue would do well to consider that the issue might not be with Zebralight, but, rather with the battery industry that seems to not have a precise specification for the so-called "18650" battery and has allowed sloppy "add-on" of so-called "protection caps", which, as Zebralight engineers point out, are of questionable benefit and questionable engineering.
For a thought experiment on this realize that modern engineering practice is going the route of tight integration of parts into the overall design goals. You see this everywhere in current design practice: For example: my Toyota Prius has an engineering specification for its tires that the tire manufacturer must conform to. A big part of the fuel economy of the Prius is tightly tied to its tires. A high end Sony Digital Camera requires a NP-FW50 battery. I have a drawer full of those batteries, some OEM Sony parts but many from a collection of China knock off factories. My dial caliber does not lie: I measure their length tip to terminal to be exactly 45mm within just error of measurement. They all conform within a .001". Look at the cell phone in your pocket right at this moment. Where would the designers of this device be if the batteries for it were +- 3 or 4 mm?
I think Zebralight, and their obviously high caliber design team is on the right track: A precise spec that they can design to. That is how you get high performance products, there is no other way to proceed. The alternative is "one size fits all", and that, my friends, is not the path to success. Since there doesn't seem to a real spec in the battery industry then I admire Zebralights guts in this matter. They have bit off the task of approaching the manufacture of a tightly integrated design into a spec that really isn't there, and then trusting their high-end customers to understand this and get batteries that meet the spec for their product.
So you need three things to make owing a MkIII work: 1.)A dial caliper. 2.) Batteries that are within spec. 3.) The wonderfully engineered light itself. I see nothing wrong with that. When I go to the tire shop for a fresh set of threads and the guy tells me 'oh it's just a Toyota any old tires will do", I will know better and can educate him about the subject matter at hand.
As poster Conner point out: The spec is on the Zebralight website. That's the spec. End of Story.
