It’s been repeated several times that 66 mm would be the absolute maximum length, even after the driver-fit issue was resolved. I believe this was again reported after the last prototype evaluation.
But I sincerely hope you are correct, and longer button-top cells such as my 30Qs (66.8 mm) and VTC4s (66.6 mm) are accommodated without risk of denting.
I’m buying anyway, of course.
But they do exist, in great quantity. And they are the recommended fodder for some lights, such as Emisar.
Many of us have quite an assortment of batteries on hand, and it’s a win-win to have flashlights that accept both.
I’m not sure if you saw my first answer, but it was about a page ago:
Lights that accept button-tops - really those that prefer them - are the cause, not the effect. The sooner that incentive to manufacture them disappears and li-ion cells are as standardized as other batteries (as they should be since the entire naming scheme for them is based on their size) the better.
I get that it sucks for people that have mostly have button-tops but the standards change for tech way faster than they have for flashlights in just about every other industry. Thankfully we don’t have to measure USB, HDMI, etc. cables before using them for anything.
And it’s good that the USB 3.0 ports on my computer also read and write USB 2.0 devices. I have quite a few of those around. Compatibility is a good thing.
And may I say funkychateau, you are doing a masterful job of that; in both this & the main FW3A thread too I might add. Reviving the discussion every month or two & dissappearing for a while after the lively debates.
Masterful my friend… masterful. :+1: . 
… But… :person_facepalming:
I’d argue that that backward compatibility shows the opposite: there was a clearly defined physical standard, not the original USB port dimensions and also a slightly different one that was hacked together for no reason, creating the actual compatibility issues.
If a light can use both that’s cool, but button tops in general are a problem looking for a solution.
Just remove the button top. It’s easy.
I have some protected button tops that I should not have ordered. I’m also quite new to all of this. Can you point me to an article or video that gives instructions on how to change these to unprotected flat tops?
I’m also interested in this if it can be done right and safe. I tought it was impossible to do so because they are spotwelded. But I m known to be wrong on occasions
…. Me too…. :+1: . 
It really isn’t safe for someone without a LOT of Li-ion experience to try and remove a spot welded button top. Very easy to short out the cell and that can be bad. The safe option is to get new flat top cells for the devices that use them and use the button tops in lights that require them, like the D18, Meteor, Q8, and so on…
That is the correct advice.
But, it’s pretty easy to remove the button, which is just spot-welded with a nickle strip to the positive terminal of the “real” flat-top unprotected cell. As long as the wrap and insulation ring is protecting the cell from shorting, then just take a pair of pliers and rip off the nickle strip. That will leave some bumps on the battery from the spot-weld. Take a dremel tool, and very gently sand them away. Done.
Of course, my advice is not to do that, unless you’re very sure of what you’re doing. At the very least, keep a bucket of water nearby to throw the cell in if things go wrong. And then run so you don’t breath any of the very toxic fumes from a lithium-ion fire.
Not all are done that way, some are literally spot welded in three places around the outer edge of the button. Those are much more difficult to remove if you don’t know what you’re doing.
Uh, totally wrong advice to throw a li-ion cell in a bucket of water! Lithium reacts with water and burns! No NO No!
I don’t have any links, sorry. If you are good with tools it should not be too hard.
First, you have to understand that the positive and negative part of the battery are very close, so caution has to be used to not touch both at the same time with anything metal. If you do, you might get a spark. No big deal, but try to avoid that. Discharging the battery to 3v or so also improves safety.
In the picture below, the positive is the red part and the negative is everything dark gray, the vast majority of the exterior. There is only the gold layer (plastic insulator) that keeps them seperate.
Button tops are stacked onto the red piece. Sometimes they are spot welded, sometimes not. Sometimes they have a longer metal strip underneath that is spot welded on each end. There are a lot of variations.
Here is a 30Q with a button top spot welded in place. It had a clear wrapper covering the stock pink wrapper. I cut away the clear wrapper and used a small screwdriver to pry the button top off.
I did not need to add a new wrapper, but I do keep some handy.
Here is a different 30Q that I removed the button from that had the metal strip under it. I cut it’s clear wrapper off, lifted the button top and then used pliers to carefully pull the spot welded strap off the battery. You might need to used a small grinder or Dremel to get rid of any burrs from the spot welds.
You might want to practice on a junk button top battery just to get an understanding of it’s construction before trying it on a good battery. Always be careful to not cause a short circuit. You also might want to use an extra piece of insulating plastic to put over the edge of the cell to make it easier to pry the button top off.
LOL Teacher, I can handle a little sarcastic jab. But it does seem that I keep responding to the same notions over and over, from new folks that haven’t read previous posts. And if I disappear for a few days, or even a week, it’s not part of a plan. I just have a pretty busy life offline. I retired four years ago, and I’m still waiting for the “leisure” part to kick in.
However, this notion that we should never accommodate button tops because doing so encourages a bastard battery configuration that “shouldn’t even exist” (because the e-cig community doesn’t use them) is a new angle …
It’s my understanding that there is no lithium metal in lithium-ion cells. So, it shouldn’t react with water. Well, that’s my understanding, but I’ve never tried it.
Lithium primary cells do contain lithium metal, so I could see how those might react.
And responding quite well I might add funkychateau. If you are not an attorney… I think you could be. And probably a darn good one too…. … :+1:
Heck, I do not ever use buttontops unless a light absolutely requires them ; but your ‘arguments’ (reasons) even got me to thinking for a bit. Then I shook off your mesmerizing & got back on track.
Good reading for sure my friend….
Take care….
Not my discussion so excuse the interruption, and I am not a chemist by trade, but I wouldn’t be taking that chance either. Elemental lithium is highly reactive, like you said, but many lithium-ions are too. My recollection from Chem1212, which granted was a long time ago, is that the lithium ions are going to react with the water pretty quickly, resulting in some sort of lithium oxide while releasing lots of hydrogen gas. This would be highly exothermic too, so lots of heat. Hydrogen gas + heat = bad news.
Besides that, I think the original premise here was that a bucket of water could be used to “put out” or otherwise contain a runaway li-ion cell, and that’s a faulty position from the outset. You won’t be stopping that internal lithium reaction with water. Its not going to stop until its out fuel/energy. So even if the water doesn’t make it worse (which I’m not convinced is true), its not really going to help either. You’ll still have a runaway li-ion cell on your hands…just now its wet.
So please, anyone who comes along reading this and decides to take some side cutters and a dremel to their stack of 18650s for any reason, do it outside. Away from everything you value. Because if something goes wrong you really only have one recourse — run away and let it burn itself out. A dead brown spot in the lawn is going to be best case here, I think.