Then I guess Hank should just add a spring bypass, better than limiting the light to only work with the shortest batteries IMHO.
You can always request us to modify the driver a bit (remove the spring), so that D2 can work with the unprotected, button top 14500 battery only.
6 Thanks
That would be great! All my button-tops are unprotected, so no issues here.
Any other side effects from a driver with no spring, besides (obviously, I guess) not working with flat-tops anymore? (not a problem for me as I donât have any)
There is no side effects, and yes, it will not work flat top battery anymore.
1 Thank
@Hank_Wang you seeing this?
8 Thanks
The springs are easily long enough to cope with an extra 3mm body length in a D1V2 fitted with a GT-FC40. There are springs both ends that must get compressed almost flat- even with a flat top 18650 inside.
(Iâm not sure if the LED / driver config makes a difference to the battery compartment space?)
But the springs are really long- the only saving is in the alloy body. See my previous post.
Thanks for the confirmation. Will order accordingly 
I think theres a fine amount of space in the d1. I have one of every color, theyâre all snug but not too tight. But I have a d4 thats pretty snug, so I get it. Hasnât dented any flat tops yet tho. Iâll take springs over a solid button contact anyday tho
Manufacturers donât add spring bypasses due to the risk of them coming loose and shorting out the light. The tail bypass isnât really an issue, but if there is a bypass at the driver spring and it comes loose, it can cause a catastrophic short.
4 Thanks
I wish Hank would set the categories as â18650 Flashlightsâ, â21700 Flashlightsâ, â18650 Tint-rampingâ, etcâŚ
1 Thank
Can we have a buck driver for single emitter like d1k/dm11 with 519A 
I just checked and thereâs 67.5mm length in the battery compartment of my D1V2 with the GT-FC40 12V driver- thatâs to the top of the post that the spring is wound around- not including the spring length on the driver.
The height of the spring on the driver post adds at least 3mm (bearing in mind mine has been squished big time), the spring in the tail cap stands 6mm high and you need to subtract itâs wire coil diameter (1.0mm) from the available length- as itâs soldered on top of the lip that contacts the body barrel.
So thatâs:
67.5mm body space
- 1.0mm tail spring diameter
= 66.5mm maximum battery length with both springs squashed dead flat!
The springs have at least ~3mm + 6mm = 9mm height uncompressed. Itâs not the spring length that limits using the button top- with 2.0mm difference in a button top vs flat top for a VTC6.
The springs will be almost completely flattened with only 1.5mm distance spare to share between them using a spot on spec 65.0mm flat top 18650.
Ya I meant to add âand the brass post/button itâs wrapped aroundâ. My bad. The springs will be pretty much flat. The post on the boost driver is a tiny bit longer than the button on the linear one. Itâs that little button that dented the button top I tried. That was on the linear driver
I only care about it having enough space to not dent a typical flat top tho. Some lights, 21700s especially, will dent flattops. As long as it doesnât do that I donât care what it does to button tops. Not sure why someone would use button tops if they donât have to tbh. Except on the D2. That I can understand.
Iâve got at least one flat top thatâs now a âconcave topâ. So I usually go for button tops as theyâre more durable- plus they can be less problematic in some chargers (where the positive terminal doesnât have a decent projection to touch the flat top.)
1 Thank
Sometimes itâs what comes with the lights: Wurkkos, Lumintop, Manker etc all ship their âwith batteryâ option with button-tops, at least the 14500-sized ones (and Wurkkos does it with the 18650s too).
And I always buy my lights in the âwith batteryâ option, feels like a waste otherwise to have an empty flashlight shipped across the world when the battery adds just a few bucks to the priceâŚ
That said, when I order batteries separately Iâve done it so far with button-tops for the 14500s (where I have at least one light that wonât take flat tops, the Manker E03H II) and flat-tops for the 18650s (where I have no such limitation).
I donât use them. All my sofirn and wurkoss button tops are sitting in fire proof-ish, static dissipative-ish boxes at 3.7-ish volts, basically waiting to get recycled. The small sizes like a 16340 I do keep because I burn through them, but the 18650s donât get used. Too many others available that are cheaper and better.
Eve 20P/25Pâs are $0.99/$1.49 this month, 35eâs, p28aâs and vtc5dâs were $3.50 last month. No reason to ever use a low drain button top in anything. Even if it requires a button Iâd use something like the vtc5dâs with a raised flat top.
Those $0.99 20Pâs are a steal. Low capacity but you donât have to worry about cycle life when itâs $0.99. Fast charge away
Thatâs maybe the one reason, but Iâll take a light that doesnât switch off if shaken over one that never dents a battery.
1 Thank
My workhorse D4V2 has done that to every VTC6 that came near it, itâs the falls it takes as it unclips from my belt. Iâve been thinking about printing a semi-soft gasket/ washer type component that would take the brunt of the blow as the battery slams down onto the brass button but Iâm worried that deforming the can could be potentially more dangerous than caving in the contact thatâs somewhat mechanically separate from the canâŚ
Thoughts?
2 Thanks