Solved: Internal resistance increase with button top VTC6 and 30Q


Quite a topical question as many of us are or will be receiving VTC6 and 30Qs with added button tops for the Q8.

What sort of internal resistance increases would you expect to see for button top versions of VTC6 and 30Q. My unprotected GAs measure around 30-35 on my XTAR Dragon, protected Keeppower 26650 5200mAh around 45-55, but my new VTC6 button tops are measuring between 81 to off the scale (>150). Doesn’t seem right?

I don’t have any flat top VTC6 or 30Qs to compare to.

Thanks in advance for any replies.

From what I’ve read, the difference in electrical resistance between flattop cell, and same cell with button top is negligible. The difference in output between two identical flashlights (slight difference in Vf etc.) is larger. I tend to believe this, but again this is only what I’ve read.

Yes, that’s why I’m a bit concerned about the high iR reading. Will also test in Lii-500 as well.

Another thing I’ve learned here by reading is that the IR measurement function of many chargers is a complete joke. Wiggle the battery and press the metal against the cell and you get different values all the time. I think with a normal decent spot weld of the button top, the cross section is sufficiently large so increase in electrical resistance is negligible.


Not to mention, the Q8 is a popular prestigious project supervised by top notch modders who know how to get the max out of a light; if something causes unnecessary reduction in output all alarms will go off… At this point that’s definitely not the case. As a matter of fact there is a very successful group buy organised by RobertB for button top 30Qs. So i’d say don’t worry about it.

In the Q8 thread there is some charts showing the difference between the lumen output of the BT 30’s and solder blob 30Q’s.

Thanks, but it’s the iR reading I’m interested in to know if I have dud cells.

Without understanding too much about this topic, I feel that measuring capacity of the cell is much more reliable, and easier for chargers to output reliable data than measuring internal resistance.

Maybe I should rephrase the original question. If you have a flat top and button top version of a VTC6 or 30Q, what is the approximate difference (according to an analysing charger or DMM) in iR between them. Surely someone has measured this?

My two randomly picked 30Qs from different sources

Flat top (Banggood): 0.040 ohm
Button top (nkon): 0.051 ohm

For comparison
VTC6 flat top: 0.035 ohm
GA flat top: 0.069 ohm

Thanks. Much appreciated. So around 25% ish more iR. I think I may be right in my concern for the iR in my BT VTC6s then.

There shouldn’t be a difference in most cases but in the case of an un-spotwelded button, there can be a large difference.

if the spread between your flats and buttons is that big either the rewrapper of the buttontop did a lousy job or you dont have real vtc6
the difference will be impossible to discern with a cheap chargers ir test.that its that large tells me something up too.

Worry not, the Q8 accepts stock unprotected GA cells :wink:

which are too common and cheap for counterfeiters to bother with.

My 30Q bt’s from BG and nkon were all around 30 mOhm
Bg 29
Nkon 30/31

Problem solved - dirty contacts were the cause. Scrubbed them hard with ear buds and methylated spirits until the iR measured came down to around 20-25mOhm on all cells. They are now all perfectly matched. Another example of why we should all use DMMs and/or analysing chargers.

Just had the exact same issue with some button top Samsung 30Qs. Very high (and all different) internal resistance values (using Miboxer C4-12). I thought maybe the button tops weren’t connected properly to the cell.

I scuffed the anode ends with 400 grit sandpaper and cleaned with rubbing alcohol.
I’m now getting the same values as I get with my regular flat top 30Qs.

Thank you stephenk and BLF! I wouldnt have thought to try that (they are brand new) I get smarter everyday here :smiley: