@pirate joe 22: I didn’t want to give them a bad name before giving them a chance to make good. They are Battery Junction dot com. I’m quite pleased and I wrote them a thank you note.
@prototype3a: thanks. I ordered a tester that says it can measure it.
Well, I did a drain test on one of the light “30Q” batteries that I got.
I drained one of them at 1A until it hit 3V. Here is the result. 1621 mAh (I assume the counter is in mAh). (I’m going to do a second one overnight at 0.5A)
Is my expectation of seeing nearly 3000 mAh off?
Not off, you should get near 3000mah, probably around 2800
I bought two 30Q cells from techaroundyou in Australia recently and they came with these markings:
INR18650-30Q
SAMSUNG SDI
6 KMT
On the can of cell 1:
R30Q
KAUA1
GAHC
CC
B14
W16
On the can of cell 2:
R30Q
KAUA1
GAHC
CC
B06
W23
Vapcell S4 Plus capacity tests:
Samsung 30Q6 18650 Cap Test #1 (2021-04-22)
Weight: 46g
Discharge 500mA
Max cell temp: 38C
Room temp: 16C
Capacity (mAh):
3046, 3083
Internal Resistance (mOhm):
26, 21
Samsung 30Q6 18650 Cap Test #2 (2021-04-23)
Weight: 46g
Discharge 1A
Max cell temp: 52C
Room temp: 17C
Capacity (mAh):
3094, 3124
Internal Resistance (mOhm):
23, 29
Personally, if you buy from a reliable source, you will likely not have to ever do all this leg work to check for authenticity. Generally speaking, if a particular battery is out of stock everywhere and one place seems to have big quantities in stock, this should be a huge red flag. Right now, Lithium Wholesale is very low on virtually every battery, so this should be an indication of the high demand.
I’ve only bought from liionwholesale.com and batteryjunction.com (this was the first time from batteryjunction). Now I’m going back and checking my liionwholesale.com batteries too.
I’m going to get that Vapcell S4 Plus charger you mentioned. You’re saying it can measure IR?
I’ve been using my Tenergy charger to test capacity by draining from “full”/4.20V to 3.00V at 1A.
Is that a pretty standard capacity test?
What’s an appropriate cutoff voltage to use when draining batteries?
My highest 30Q cell (from another order—used but not heavily) was 2400 mAh.
Most of the cells from this order seem to be around the 1600 mAh range.
1600mAh is wayyyyyy too low and even 2400mAh is too low for a genuine 30Q unless it’s been very heavily used. Are you reading 4.20v from the charger or a DMM? If it’s the charger have you confirmed it with a DMM? Perhaps your charger is not working well?
There’s an international battery shortage and a lot of re-wraps about. I’m UK based and only buy batteries from this lot. The guy running Fogstar has been tenacious since day one, batch testing and even visiting factories.
No affinity to, or gratuities from the seller, he just cares very much about the battery safety of Li-ion, particularly in our high draw multi cell vapes and lights.
DMM - what is a DMM? Sorry, I’m new to testing batteries.
Here’s a pic of the best test result:
This is using this charger to drain.
I just bought this tester but I haven’t made a circuit yet to actually hook it up. It came with no cables.
DMM is a digital multimeter which allows you to read voltage, current, and ohms. Your readings are so far off that my thinking is that your Tenergy is the the problem. Most counterfeits these days seem to do better than what you’re getting so confirming the starting voltage would be good.
Sorry to ask the obvious but you’re not charging the batteries using the LiFe setting are you? That would account for their low capacities. When you start the discharge does the display show 4.2v’s or 3.6v’s?
Never apologize for asking. I’m using a Nitecore D4 charger. It achieves 4.20V upon completion. Here’s a pic.
Ah, a multi meter. I didn’t know the “DMM” abbreviation. I happen to have one. This is after 6 hours out of the charger.
Well it’s definitely not the case that the batteries were discharged when they were less than fully charged. Too bad because that would have been an easy thing to fix 
Always weigh your batteries and check the sellers advertised weight BEFORE buying, if no weight is stated, do not buy.
.
I only buy 30Q’s from a few stores that Guarantee Authenticity, NEVER— Ebay, BanGood, AliExpress, or similar stores.
Good batteries are not cheaply priced.
.
.
I’m not an expert here, but I measured capacity differs depending on the manufacturer and the specific battery model (they are usually listed in the datasheet for that specific battery)…
But based on my limited experience reading several battery datasheets, for 18650s, it’s usually 0.2C (1/5th of the capacity), ie. discharge at 1/5th the nominal capacity.
So for a 3000mAh battery, discharge it at 3000/5 = 0.6Amp, and it seems for many 18650s, the end-voltage is 2.50v, to get the manufacturer rated capacity (I see a few 18650s that have an end-discharge voltage of 2.65v or 2.75v, and a very few that even have and end-discharge voltage of 2.00v — I think the LG HG2 has this).
But for simplicity’s sake, when I check an 18650 battery’s capacity, I discharge at 0.5A down to 2.50v (can program the setting in the SkyRC MC3000 analyzing charger).
Discharging to 3.00v will probably lose a small amount of capacity only though - perhaps 100mAh more or less (compared to discharging down to 2.50v). However, if it’s a low-drain cell, then there may be a more noticeable difference discharging at 1A compared to discharging at a lower 0.5A. But for most high-drain and good medium drain cells, the capacity tested at 1A vs at 0.5A is minimal (as per my experience, discharging using my MC3000 charger)…
Since my purpose is comparing one of my cells to another and to itself over time, I think I will standardize on the 1A discharge to 3.00V, and I’ll simply expect to be under the manufacturer’s rating by a bit. The rating should give me a decent idea of the cell’s performance in a flashlight. 1A also allows me to test twice as fast as 0.5A 
Be aware that most every cheap discharger is only a two point connection and this will terminate the discharge prematurely due to IR losses in the wires and contacts. Using higher currents will exacerbate this effect.
My button top 30q’s all way 46.75gram give or take a few 100’s of a gram. If I was the OP I’d take the clear & pink wrapper off a cell to see if Samsung’s unique codes are underneath. Given all his cells are 42g. Damn mine field the battery market. I think unless you can do current discharge tests to see what amps they can sustain I’d first examine them phisically.