http://na.industrial.panasonic.com/sites/default/pidsa/files/ur18650zy.pdf
At 1amp discharge and 2.75V cutoff your equipment should measure less than 2500mAh, see the datasheet. your opus measures "2650-2680mAh", that's at least 200mAh off. that's a tolerance of >8%.
For a 5200mAh cell, your opus would measure anything between 4780 < 5200 < 5620 mAh, that's a range of ~1000mAh on a single 18650.
Not accurate at all.
Still, how can you not see that I get the same numbers on two different chargers from two different manufacturers?
But, as told earlier in this thread, it’s seems like the discharge and discharge and refresh mode gives different results. The first Samsung battery has now completed a full “normal” discharge on the C3100, and it’s almost 3000mAh.
So it’s seems like my Liitokala Lii-260 uses a discharge refresh mode type of thing.
So maybe the Samsung batteries is not fake. But the Ultrafire batteries, rated at 5200mAh, only gives around 1400-1500mAh, so they are not rated correctly. What ever you say.
I thought no battery can go over 3400mAh in single 18650…the best of the best that is the HIGHEST mAh rating you can squeeze into a single 18650 platform
Any of these insane high mAh ratings are just chimAh ratings they slap on the side to entice people who don’t know they have the largest capacity…if you get 1400-1500 per battery that is still useable (the actual fakes people have seen here with tiny li po batts inside a hollowed out 18650 shell w/ some sort of powder inside for weight read in the mid 100mAh range!)…just low, but would you trust em…nope
Two of the sellers has offer full refund now (Ultrafire 4x and 8x). But they want me to ship them back to the UK, and the shipping cost would be almost as much as I paid for the batteries. But luckely E-bay told the seller that he have to pay for the shipping back…so then I have to see, if he still want to pay for the shipping, and get the battery back, or just refund me.
The two sellers: gothic_household and rgbstore12 is the same seller. Since I got the address where they wanted me to send the batteries back, I saw that it was the same. Sure the last Ultafire 8x seller i the same also.
I think his 5200mah batteries are 26650's not 18650's ...
Ebay is a horrible place for people to buy lights and batteries unless you're really really smart .
Noobs need to avoid the joint like the plague .I have no idea why people are so attracted to it . The really great deals are usually found here on this site ..almost never on ebay .
95% of all noobs who come praising some light they picked up cheap on ebay only to find out 3 weeks later that they bought a dull stick.
Avoid Ebay
But the batteries I have from Ultrafire has 5200mAh printed on 18650 batteries, with a actual mAh on 1400-1500.
It can be good and it can be bad. But I think it has been worse. Most of my stuff is got from Ebay or DealExtreme, and I have been lucky with lots of the old stuff. I have tested some of my old Trustfire batteries, some around 8 years old, some has been in my car, cold like h*** in the winter, hot like h*** in the summer in the sun, and still, they had over 2000mAh on them (after a recharge, then a discharge) after so many years. (it’s 2200mAh batteries), and I had some TrustFire 3000mAh with a actual mAh of around 2800.
And my flashlights, back in the days, I actually got real Ultrafire WF-501B with actual lumen of 700-900. Now you get 2-3000 lumen flashlights, that actually is 600-800 lumen, if you are lucky.
The rating sytem on Ebay and on other site is not correct, since (me included) often give feedback when I get the product, few can test lumen or real mAh before giving feedback. So then the feedback is good, maybe fast shipment, good price etc.
Then you can’t change the feedback after you find out the truth.
I agree with Boaz, also I think this is how most of us landed here.
As a side note, did you considered that:
Capacity depends on many factor, but considering a perfect world with the EXACT PERFECT same battery, charged at the same voltage, mainly on the discharge cut off voltage. So if OPUS cut’s off at 3.00V and another one cuts off at 2.67V, you will get more mAh from the latter.
ALso drawn current affects capacity, as you all know. And also discharged capacity is more accurate than charged one.
Of course there will be difference. That because etc Sanyo uses a range from 2450 - 2600 on their UR18650ZY, depending of temperature in the room etc. So of my 50 UR18650ZY, I will guaranteed never see the same number twice.
But the actual discharge mAh should stay within the limits of 2450 - 2600 (aka 2699). And my Sanyo batteries are. The last two new i tested was around 2550+.
The Samsung test I did yesterday, had to be wrong, at least the two batteries I tested first. When I tested all four on charge discharge, I get 2884, 2886, 2874, 2850 after three full cycles. So thats within the margin.
I have sent a sorry mail to the seller, and closed the case.
On the seller that have sold me Ultrafire batteries…they can’t get away with it, so I have got some of my money back today, still waiting for one seller, and then there still is lots of Ultrafire batteries in the mail (ordered a long time ago) that will arrive, then tested, then I will open a case, if the batteries is not 3500mAh batteries then 
One seller (two “stores”) wanted me to send the batteries back, 12 x 18650 5200mAh with a actual mAh at 1400-1500. I checked with the postal office, and I had to pay £28 if I wanted to send them to the UK from Norway as registered mail.
He did refund my money right away then. Since Ebay demands that the seller also pays the shipping back to them.
unless you are running a test,name and shame sting operation its easy to avoid this garbage.the highest real capacity i have seen for 14500 is 840 and thats a sanyo.
3600 for 18650.
you know its B.S if stated higher and esp if “fire” is in the name!
I gues the description is almost correct:
gothic_household – 8x UltraFire 18650 3.7v 5200mAh Li-ion = 5200/8=650mAh per battery 
I got two 26650 7800 red ultrafire batteries, ordered for a long time ago this week.
Actual mAh after charge - discharge - charge test on Opus BT-C3100 and LiitoKala Lii500 was 2200 and 2300 mAh.
This is from Ebay seller directsales-hk.
Also got some red AA (3000mAh) and AAA (1800mAh) from the same seller, they had an actual mAh of 300 and 200.
i am the new owner of 2x lii-500 from Ali Express (~$24)
and would like to confer with other owners of the lii-500
how low does your lii-500 discharge before charging and to how high
i need more time with mine
i see 3.50v on the discharge
and 4.21v - 4.22v for the full charge
i started a mini review of the lii-500
BTW once i bought x…FIRE cells (got my money back) and i guess they are ~1000mAh
My discharge down to 3V and charge up to 4.20-4.21V. So if your stops at 3.5V, something is not right.
i might have missed end of the discharge i need more time with it
If you are seeing 3.5v after the battery has had time to rest than that is normal. And we’re only talking several minutes as opposed to hours.
both of my lii-500 discharge to 2.82v exactly and then go in to a charge cycle
that is with new Sanyo NCR18650BF
i am now charging 1 at 500ma
and 1 at 1amp
so to fully understand this since in theory i can go down to 2.5v (i probably never will) i will never see 3400mAh as the end charge because it only started at 2.82v and in its best guesstimate it (should) display less then 3400mAh
And amazon?
Simple rule of thumb, If it`s got FIRE in the name of the cell, dont buy it unless you are 100% certain they are not fake, there are lots of other brands.
Also other CPF member from Norway or EU, Should be able to supply you with some local reputable seller that they have used in the past.
John.
One of the 1st lessons learned here was don’t buy a battery with the word fire in it. Still holds true…
you can find Samsung, Sanyo, LG, Panasonic and Sony cells for are decent price without running into fakes
But buying batteries on Ebay from strange sellers you run too often into fakes
In general over 99.9% of those cheap fire cells are fake if they are rated above 3500mAh
I bought plenty of cells over Banggood and Gearbest and they are all 100% original
there are way over hundered cell types tested on this website from HKJ
http://lygte-info.dk/review/batteries2012/Common18650comparator.php
you can see how good the cells are
Samsung 18650-30Q are great cells and relatively cheap