Problem with IOS T10B Host and 2x18650


I just got a light that uses IOS’s T10B host.

It works ok without the extension tube and with 2x18350 batteries, but I have to screw the tailcap in really hard… I mean REALLY hard, in order to get it to work.

However, when I use the extension tube and 2x18650 batteries, I can’t get the light to come on at all.

Looking at the design, it has anodized threads (both male and female) with just the ends of the tubes unanodized, and then inside the mating tube, there’s an unanodized ridge/shelf.

My theory is that they made the threads to shallow/short, which means that, in the case of the non-extended tube, you have to screw the tailcap in super hard… as I said almost too hard, to the point I worry about damaging my batteries.

I think that this is the same problem with the extension tube. Either where it mates to the original body tube, or where it mates with the tailcap.

Has anyone encountered something like this? I’m wondering if it’d be possible to scratch the anodization off of the threads, and if I could do that, would that elminate the problem?

This is a tail clicky, no electronic switch, so it doesn’t seem that lockout would be needed?


I don’t have your light. You might be able to make a copper washer out of a solid piece of copper wire. Ends soldered so it’s a more sturdy circle.

Do you mean to position that against the ridge on the inside so that the unanodized male end contacts the ridge sooner?

The problem is iOS! You have to buy Apples proprietary tailcap and charge through the Lighting port. 0:)

Assemble the light with the tailcap removed and the batteries installed. If there is a spring on the driver gently push the batteries down until they will not push in further. Take note whether they are below or above the battery tube. With the tailcap push on the spring until it bottoms. Take note how far the spring compresses in relationship to where the tailcap bottoms on the battery tube. From this you should be able to determine whether the batteries are to long. With the tailcap removed will the light work by putting a metal object from the end of the battery to the top off the battery tube? The above must be done with the two batteries installed.

If I jumper from the battery negative to the unanodized end of the battery tube (without the tailcap), the light turns on, regardless of which pairs of batteries I use.

But, I have one pair of batteries that always works, with both batteries being laptop pulls.

Other pairs of batteries, both protected and unprotected (2xEfest 18650, 2xCGR18650 (gray), 2xUF18650), don’t work at all.

This is still really puzzling!

Edit: All batteries, both the pair that work, and the pairs that don’t work, are button tops.

I built a T10 host up, no extension tube, and similar problem - got to tighten the tailcap pretty good for it to work, and can't do a conventional tailcap amp measurement - the finish is gorgeous on these hosts, but it's got to be too much anodizing. Never tried anything onthe threads because it works fine, but wondering if maybe wire brushing the threads to get off some of the anodizing would help. Think you can use chemicals as well - I know there's been posts about it - forgot what they used.

I also got a T10B host, but had no time to work with it yet.

Would it be possible to post a link to the driver used. It sounds like the batteries are to long. To make proper contact between the tailcap and battery tube it is pushing on the driver to much causing it not to work. If you can disassemble the switch and remove the cover on the spring, this may allow the tailcap to screw on properly without distorting the driver. If the driver has a spring on it this can sometimes be removed and a suitable small round piece off copper or solder blob used so that longer batteries can be used.

MrsDNF may be on the right track - forgot, I had all sorts of issues assemblying that light - I grinded down the pill to make it fit, and have proper spacing for the battery, yikes - it was a while ago...


If you ever get around to working with the T10B, especially with the extension tube and 2x18650, can you post about it?


I think that it’s this IOS driver:

[Did this driver use to be a “3.5 amp” driver? IOS shows it as a 4.5 amp driver?]

but the separate contact board wasn’t used. Instead, the builder put a copper nub on the bottom of the driver PCB, i.e., so it’s now a 1-board driver, rather than a driver+contact board, so there’s no spring on the positive end.

The tailcap has a cap on the spring. I’ll try to remove the cap and just use the spring.


Wow, Yes - this was the 3.5A driver I'm using in Shockers now... Interesting... ? He no longer offers the 3.5A version, looks like. Probably just resistor changes...

Oh - this must be one of those custom MT-G2 builds. Think a guy on CPF was building/selling a run of them. Was wondering how they got that driver to fit into that pill - I tried it, but with the contact board, it's too big.... Hank actually push's this combo of emitter, host, and driver.

It does definitely sound like your batteries are to long. MrsDNF and Tom E has given you some good things to try. You could make a washer to fit between the tail cap and body of the light. Removing the anodizing is easy enough if you decide to go that route.

Drain cleaner, specifically ones containing lye. Or you can use greased lightning. I've never done it, so I can't comment any further. I used a dremel with a wire wheel.


Yes, drove me crazy this morning searching for “3.5 amp”, “3.5a”, etc. trying to find a link to post here.

Anyway, this is the one from CPF, and as I said, he just ditched the contact board and somehow put a copper nub in the middle of the battery side of the PCB.

I have never tried the greased lightning method. The Lye (caustic soda) method works quick and easy. You should be able to find it in your local Ace. Drain Cleaners & Drain Clog Remover at Ace Hardware
They sell them individually in the store.

I disassembled the tailcap switch, and I think that I see the problem. The spring that goes under the cap is really short. When I re-assemble the switch, but without the cap, the spring barely sticks out higher than the copper collar and the black plastic collar that surround the spring :(!!

When I try the tailcap with the metal cap removed, even the pair of batteries that work when the tailcap has the cap in it don’t work… probably because that spring doesn’t even touch the battery negative.

I’m now thinking that the solution should be use a longer spring… one of the ones that don’t taper?

Oh boy, often wondered where I could get tailcap springs - don't think I ever saw them sold anywhere. They are longer than the usual, and like you say, don't taper usually.

I’ve asked the CPF builder to contact Hank about this. This seems like a design flaw. I haven’t measured how much it sticks out above the collar, but I’d guesstimate that it’s like 1/8 - 1/4”. Not much room for error (battery variations).

I'll check my T10B this eve, but the T10 single cell host has good spring contact with the brass cap - it compresses when assembled.