So I just spent a large chunk o’ change on a Malkoff Devices MD3 “Wildcat” and the matching MD-4 body (accepts four CR123 lithium cells or two 18650 rechargeable cells). I also purchased a pair of Panasonic NCR18650B Protected 3400mAh for this light.
Now in the body of Malkoff’s advertisement for the MD-4 body, it states “It has come to our attention that some of the 3400 mah batteries that are sold as 18650’s are not true 18650’s. They are larger than 18mm in diameter. Please note that cells larger than 18mm may not fit the 18.6mm ID of the body.”
Well, of course, the cells I got don’t fit. Now I don’t know how much more genuine I could have gotten than these Panasonics I purchased from Mountain Electronics!! I know you’re not supposed to run unprotected 18650’s in series- so what is one supposed to do?? I assume the extra diameter is due to the conductor running up the side of the battery- and the sleeving covering it…
Should I get a hone and bore the interior out a bit?? Doesn’t seem to me I should have to do that on an expensive flashlight!
Wes
same thing happened to me about a month ago - although i knew my cells wouldnt fit ahead of time since i measured
i bought 2x efest protected 2600mah 18650s that were listed as having 18.2-18.3mm diameter… they fit snug and were $12 shipped on ebay for the pair (sold out now)
you could bore the tube out if you wanted, i saw a few members on cpf did so with sucess
it is annoying that widespread panasonic 3400s dont fit but i guess the only options are to use diff batteries, or bore out the tube
another flashaholic problem |(
i got same experience when try to put panny 3400mAh protected on some of my light because the cells is just too long 
That's a real bummer. Check your PMs.
Also, "Please note that cells larger than 18mm may not fit the 18.6mm ID of the body.”"
What? How is it that anything larger than 18mm may not into an 18.6mm ID? I'm guessing that it's not really an 18.6mm ID or it's a typo. That said, those cells are around 18.67-18.7mm so they wouldn't fit into a 18.6mm ID anyways. Almost all protected cells are wider than 18.6mm due to the extra wrapper and metal strip running up the side.
Check my PM’s? I assume you mean private messages? I have none….
This seems to be a prevalent enough problem that anyone manufacturing body tubes should take this into account… it’s not like it’s a new problem just popping up!!
I will also take away points from Malkoff’s website in that there is no way to contact him!! No ‘contact us’ link, no contact info or phone number or email address…. Not very professional.
O.K., 2nd edit to this comment… I finally found contact info by going to ‘testimonials’… not exactly the place I’d go to look for contact information!
Wes
Your problem with the cells not fitting is really a problem with the manufacturer of the light. A protected 18650 is officially known as an “R19670”. If everyone followed the conventions, including us, there would be fewer problems.
To me there should be no excuse for manufacturers of chargers and lights that do not allow for an R19670 to fit their device!
Here is a quote on the specification, as referred to by Wikipedia
“Most manufactures advertise both bare R18650 cells and protected R19670 batteries as being 18650 batteries for historic reasons. When 18650 cells first came out many years ago, they were only available in the unprotected format so the 18650 size designation was correct. But over time, protection circuits were added to the 18650 cell for safety reasons. Adding the protection circuit increased the size of the resulting battery to 19670. Hence the proper size designation for a protected 18650 cell is 19670. But because these protected batteries were built around the original 18650 cells, most of the suppliers continued to use the older incorrect 18650 designation instead of the newer correct 19670 designation. This has proven to be very confusing to most customers.”
Thanks for the information, Dchomak-
Do you have a suggested solution- other than the manufacturer correctly dimensioning their body tubes? Because this is an after the fact problem, and I’m stuck trying to figure out how to deal with it now. Any batteries (protected rechargeables) that will work- other than CR’s??
Wes
The Panasonics do seem to be a little larger than some of the other brands. Maybe a cell change. It’s a shame though, the Panasonics are very good.
Any suggestions for replacements? Yeah, it really stinks to buy a super premium flashlight- and not be able to put the best batteries in it!
Wes
Maybe some protected 17650 or 16650 cells... but you lose capacity vs. a good 18650.
Good Old TrustFire? At least they seem to fit whatever I've tried them in. 
so you can’t get them in or they won’t come out?
Well, I’m ashamed to admit it, but I got them to fit…. I took off the stick-on label, a light coat of silicon grease on the inside of the tube- and with the help of a wood dowel, by golly- I got ’em in there!! I do not expect them to come out as easily… or gracefully… or reuse-ably!!
I’m going to purchase a Flex-Hone and see if I can’t hone out the cylinder a bit… though I’m still awaiting a response from Malkoff to see what he has to say. I maintain this is a known problem, and he should have made the tube a half mm larger- to accomodate protected cells, which is what should be in a 2-cell tube!!
To add insult to injury, I ordered 2 sets of these batteries from Mountain Electronics LLC… but when the well-packaged envelope arrived yesterday, the end of the bubble mailer was torn off- and only 1 of the 2 sets of batteries enclosed! Had to be USPS fault. Of course, since the package was not insured, they won’t accept a claim, even though they mangled the envelope.
To Mountain Electronics LLC VERY GOOD CREDIT, I spoke at length with them, and they were MOST helpful, and are sending me another set of batteries, and they suggested possibly using 17650 or 16650 cells… which I’m also going to investigate. Would just like to say that Mountain Electronics earned my future business today FOR SURE- and I would highly recommend them!!
Wes
Flashlight manufactures should be allowed no excuse.
You can enlarge the battery tube with sandpaper & a wood dowel. budgetlightforum.com/node/18473#comment-324577
Hey just wanted to comment that this thread taught me alot. I wondered what the differences were in sizing & how to use the protected vs non. Now its clear to me. Good info for a newbie. Thanks.
Also, I have seen those magnetic spacers & plastic sleeves. I am assuming that those are to help if someone has batteries that don’t fit, they can use a smaller cells of the same voltage to fit their light. Seems like its kinda a ghetto rig?
be very VERY careful with magnets
if the magnet touches the side of the inside of the flashlight tube the batteries could short out - very dangerous situation if the batteries are unprotected
that's nice to know.
If you want a quick fix buy the 3400mAh EagleTac 18650s (at: GG, illuGear, LJ, eBay).
at 18.4mm (HKJ measurement)... these may work.
cf. also to "Diameter of Battery" 2nd Chart down. (HKJ)
yes indeed. I read that a short while ago. One fellow said to try and super glue them in place. Very nice to know. 
I just received a replacement tube from Gene Malkoff- and also received the 2nd set of batteries from Mountain that had been lost out of the original package (Thanks, USPS!! NOT!)- and to my surprise, everything fit up properly!!! To be honest, I didn’t think the replacement tube would be any different. Not being able to easily remove the installed batteries from the original tube, I can’t accurately measure the tubes to compare- or the batteries, but heck- I’m just happy to have the whole thing together as it should be.
Again, my thanks to Gene Malkoff for sending me a replacement tube- and also to Mountain Electronics LLC for helping me resolve the lost battery issue promptly, even though it wasn’t their fault.
Merry Christmas, everyone!
… or Happy Holidays- you choose! 
Wes