Did the battery voltage at discharge stop at 3.7 volts or did it rebound to that voltage after stopping at the cut of voltage?
@MRsDNF, That first discharge it was left alone overnight at a 500ma discharge. The battery could have dipped low, but once the draw was off I think the voltage could have came back up without the load since it was left so long. I’m guessing if I try better batteries in it, it won’t have some awful results. I wish I could find some good 10440s.
I have seen weird behavior with some poor quality protected cells. Also There are a few times when, for whatever reason, there was a poor electrical contact between the cell and the charger.
Poor cells will show a higher cutoff voltage because the charger sees only the voltage on the outside of the cell. That voltage is the internal voltage minus the voltage drop across the internal resistance. So good quality cells, and discharging at lower currents will result in cells sitting in the cradle with higher “recovered” voltages after the test is completed.
Yeah, I see that one on Amazon (ships from Amazon too). What's the deal with the 3400? What's the difference?
-Garry
Apparently its a 3100 v. 2.1, with exclusive numbering for one supplier. So apart from the number, nothing. Theres a post here somewhere reagarding it, but Henry Xu was contacted, as yet I havent seen an official response from him regarding the 3400, nor can I find any official mention of a 3400.
I can officially confirm that Henry Xu has confirmed through my email to him that they are basically the same, only re-labeled at the request of an Ebay vendor.
I just got mine charger today.
It took more time, then I expected, but I’m glad I got it.
Hello everybody !
I’m a little disappointed… I bought my BT-C3100 v2.0 in july and one month later there is a new version 
So I ask myself to sell my opus an buy the new one.
But is it a good idea ? I do not use my opus with the power supply provided but with my 40amps ham radio power supply, so I think all my measures with the opus are accurate ?
What will I get if I go for the new one ? Does it worth the cost ?
I read somewhere some of latest dispatched v2.0 already had some improvements. Mine has been shipped on june the 21st… is it an improved v2.0 ? (I can’t find any manufactured date anywhere) ?
Please, help me make my mind !
Thanks guys !
If you need another / backup charger, you can sell or gift yours, than go for it.
Otherwise it’s a 42$ extra charge to get a slightly better - but not perfect - charger. And not everything is fixed with v2.1. and the voltage switch still “hidden”.
FYI:
It took 8 days from my order to get the Opus in the mail.
The notification stated that it will be another 12-25 days for delivery to the USA via Netherlands Post.
The shipper also claimed the full price instead of the GB price. My PP invoice was the GB price. Seems strange.
Hi majszter, hope you can like it, and thanks for your supporting for GearBest. :party:
Hi NightSpy, if you need any help, please be free to PM me with your order number, at your service. 
I think the customs form had the amount of the BT-3100 v2.1 as $28US on the PostNL shipment. I know it wasn’t over $30, since I thought right away I overpaid since the forms value was too low. I know countries with VAT would have appreciated that, but I didn’t.
How long must DHL wait to actually ship me my second order? Is there a cutoff time to get my money back if it got returned or lost? Almost to a month now.
You might find this consoling: (sorry, I can’t copy/paste just the link alone)
Merchants Face Delivery Delays from China Suppliers
By Ina Steiner
September 25, 2014
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Merchants are facing delays in shipments from China that are going through Hong Kong. The issue is impacting some sellers as they source inventory for the holiday shopping season, though EcommerceBytes has yet to determine the scale of the problem.
Suppliers in China are telling merchants there was a corruption scandal involving jewelry-smuggling in Shenzhen Huanggang recently, followed by customs officers in Man Kam seizing 2 tons of counterfeit currency last week.
As a result, suppliers are reporting, Hong Kong customs is checking a greater percentage of shipments before allowing them to leave the country.
One small business that imports items from China on a bi-weekly basis using DHL said he’s getting reports of “Customs Clearance Delays” on the latest shipment. He received the following email from his supplier:
There’s a very serious jewelry smuggling case found in Shenzhen port recently, 300 people involved in corruption, and almost at the same time in another customs, 2 tons of counterfeit money were found.
As result of these 2 serious cases, all the customs are very strictly, they inspect the goods extremely carefully, so the recent express declaration of export goods has been seriously delayed, especially for the goods that shipped from Hong Kong via DHL, FEDEX, UPS, TNT.
This problem happens on every package, we are also very worried about it, we have many packages that are held on customs. We can only wait.
For the future shipment, we will have to use other local express company (like Hangzhou FedEx, Guangzhou UPS), they have directly flight to US, no need to go through Hong Kong port, and these customs will be not so strictly.
It’s a very bad news for us. We will keep checking on this shipment.
Another reader who reported the problem to us wrote, “Customs is checking 90%+ of vehicles….entering the DHL facility. Affected buyers will see only the tracking event Shipment Information Received and may think they are being scammed by their suppliers. They are not. It’s a legit issue for suppliers and there isn’t anything they can do.”
The seller said he expects the problem will be further exacerbated because of the National Golden Week holiday. “Oct 1-7 is a 7 day national holiday in China….So, once this clears up….boom….7 more days of supply shortage,” he said.
When contacted late Wednesday afternoon, a spokesperson for DHL in the United States said she was unaware of the issue and would check with colleagues in Asia.
Just got in my v2.1, and still have a v2.0. The v2.0 version reads voltage 0.03v low, so a fresh full charged cell off the Opus tests at 4.23v on my Fluke meter. The new v2.1 reads 0.06v too high, so the v2.1 says 4.20 but the Fluke meter says 4.14v, sometime 4.13v.
So the new v2.1 is under-charging all my LiIon cells at an amount I think is unacceptable. Anyone else having this issue? I raised a ticket on it with GearBest. HKJ in his review thread said his V2.1 he tested was dead-on, pretty much. I have lots of chargers and almost all seem to be off a bit, but none more than either Opus. Is it just my two?
I just got a v2.1 and my cells come off at about 4.17v. I’m ok with this since it’s less stressful for the cells and it’s not as if I need every last mAh from them. I have a Nitecore I2 where some cells come off at 4.225 (as measured on my Fluke) and I definitely like that a lot less. When using the I2 I try to pull the cells before the charger indicates that they’re fully charged but it’s a pain.
I have a number of other chargers where the cells come off at ~4.20 but for me the Opus works well enough and I can charge 4 at a time. I can parallel charge 4+ cells on it but the Opus is more convenient to use.
@Tom E, when you go to the charger you see 4.2v, and they test lower. So, do you pop them back in the charger? I think it would read the same as the meter, but then it would switch to saying full instead of trying to charge them more. I think I’ve seen my batteries do that.
I have a 14500 cell just charged on the v2.0 and it reads 4.21v on the meter, 4.18v on the v2.0, and 4.28v on the v2.1. So, a 0.10v difference between the two, but the v2.1 is reading 0.07v high, so it will consistently under-charge by 0.06v-0.07v. What the Opus displays is that it thinks is the battery level, so it will adjust the charge cycle and terminate the cycle based on that reading - I've proven this over and over.
The designer/engineer of the Opus posted in another thread the unit has an accuracy of +/- 0.05v, so my v2.1 seems to be out of tolerance according to his spec, which is rather a coarse spec to begin with. Of course this spec is not in the product listing anywhere it's sold.
Got my Opus 2.1 3 days ago, and I tested the accuracy, and I should say it’s pretty much accurate.
Actually Opus 2.1 made me realize that my cheap DMM is a garbage.
When I charge my 18650 with a cheap Chinese charger, my cheap DMM reads 4.17v, but Opus reads 4.27v.
Curious which one is to blame, I borrowed my brother’s old Sanwa, which is known to be very accurate, and it actually reads 4.26-4.27v. The Sanwa is analog , so I could not read the exact numbers, but from the needle position, I can see it’s about 4.26-4.27v (actually more like towards 4.27v from the needle position)
Not satisfied, I borrowed his Fluke (also analog), and it reads the same about 4.27v.
That’s where I know my DMM is a garbage, and Opus reading is pretty much accurate.
Charging my 18650 with Opus 2.1, it reads 4.18v on my Opus, and approx 4.17-4.18v in Sanwa & Fluke.
Oh boy - you and HKJ got a good one then... Wonder if mine is the 1 of 100 then 
.
Tom E I’ve got the same situation v2.1 reads 0.07v too high. v2.0 is normal reads same my meter. Created ticket at the gearbest waiting…