Thanks for clarifying. Yes, 3-4% I have to throw into my runtime equations. My XTAR WPII terminates right at 4.20V dead on every time as does my new little XTAR MC0. With the glowing reviews of the Opus, I wasn’t expecting such poor correlation in such a basic function.
+1 - me too
From post #204 here: https://budgetlightforum.com/t/-/24621, the engineer/designer, Henry Xu replied to my questions and said this:
Tom: The charger will charge each cell to 4.20v before terminate the charging processing. Our charger doesn’t supply trickle charge current, so when it stopped charging, the cell voltage will re-settle by itself, and after 12hours, cell voltage can be 4.16v display. So concerning volt meter accuracy issue, please do this: make a charge cycle, and after is shows full, you take out the battery and measure the battery voltage with a DMM. We have +/-0.05v tolerance ( internal control is +/-0.03v at 4.2v condition). There will be volt display variant due to internal voltage resister network components variance reason. With your case, displayed value of 4.18 for 4.2v is possible with this charger.
Sounds to me like you are due a replacement according to this rational and your post #250 above.
And my cells read within .02 volts after charging and a rest time of 24 hours. Again, using my XTAR chargers.
As a matter of fact, I have a 14500 holding within .03V for several days when installed in a device!
Does Xu needs a few quality XTAR cells to test with instead of cheap ChineseLiIon cells.
Mine should arrive tomorrow. I will be upset if it ends at 4.15V.
Both Nitecore and VP2 terminate at 4.17~4.18V. Even my old $4 charger is able to terminate at 4.2V.
Isn’t it better to terminate charge a little early to preserve the life of the cells and get more cycles out of them? Just asking, I’ve read in the battery university that you should keep a cell at peak 4.2v cell voltage as little time as possible to minimise stress and prolong life.
4.15 does indeed sound a little on the low side.
I wouldn’t mind a resting voltage of a cell even at 4.14v (overnight, on each test). In these tests I made on protected Soshine 2900mah cells, it still had discharge capacities ranging from 2871mah to 2915mah, using 1A, 3A and 5A discharge rates.
See for yourself in the review link below:
Capacity is one thing, but internal resistance is another important attribute for me, resulting in lower performance for a partially depleted cell. If that 4.14v was 4.20v, what would the capacity be then? It's kind of hard to compare when there's only one level with data. I've had KK 26650 4000's test at over 4400 mAh, so higher results than labeled is common.
Hi Tom E,
I was only pointing out that having a cell that rests at a “low” 4.14v does not mean a bad cell, nor will a cell that rests at 4.19v be necessarily better and will show way higher than its rating, at least in my various tests with different chargers and cells.
As for KK cells, they have historically from 5 to 10% higher capacities than their rated capacities, as I have owned some before, but seldom with name brand 18650s, mostly lower by an average of 2 to 4%.
Your charger might just be defective as you are saying, unfortunately.
If it's defective, Henry hasn't answered my pm, hasn't been in the forum in 11 weeks, and I have no clue who manufacturers these things ?? Not sure if Henry ever mentioned it.
GearBest just this morn offered two options:
- $15 refund, I assume in store credit, which will be no problem anyway for me
- I can buy another Opus BT-3100 v2.1 for $25
I suppose no guarantee the new one will be any better than the one I have... My only choice is the $15 because I'm not taking this gamble again - that's for sure. I was seriously thinking of configuring it for 4.35v so it charges to about 4.28v, then leave them in for an extra 12 hrs to trickle drain... Might work 
. Should drain to about 4.24v which is within their tolerance. Of course the CC/CV cycle may shorten the cell life a bit... Actually it's bout perfect for 4.30v cells that way and I may have a couple of them...
I'm trying to find an up-side 
.
I would buy the second one for $25, in a second!
Not for anything else, but I have 2Xv2.0’s, 2Xv2.1’s and all of them have been performing very well, don’t have the same problems as yours.
And Gearbest has almost sold a thousand units so far of both versions, and if complaints similar to yours here in this forum is an accurate gauge, problems such as yours can be considered an ‘isolated incident’ so to speak, (if I am not mistaken, not more than 4 individuals) as they are a very small percentage compared to the total number of sold chargers.
My point is, buying another Opus AND getting another DUD unit is quiet remote.
If you buy and you do get a dud, play the lottery man.
Overwhelming % of units sold aren't even tested for this I'm sure, so, owners aren't aware. It's dangerous to assume only the 2-4 units reported here are the only ones, or represent the below 1% of total units sold. If they carelessly sell units that are 0.07v reading high, are they selling units that are 0.07v low? What about 0.09v low? What if all your cells are charged to 4.28v instead of 4.20v? Will a typical buyer even be aware of that?
Where I work, we'll have a firmware/software bug, fairly significant that breaks a functionality and it's out there for years in 100's of units sold, unreported, at least to us. Why? Lots of reasons - users find a work-around or simply stop using the feature and don't want to be bothered reporting it, or they simply never used the feature, or use it in a way to cause the bug. Maybe it takes over 1,000 sold units to get the single one report in of the bug after 2-3 years, but 100% of the units sold had the bug.
Since Henry Xu had been very active here, and appeared to make sincere efforts to address our concerns then, I'm hoping by raising this issue, that it gets investigated at least. I asked GearBest in my CS reply if they could report it to their supplier. I should check the box/manual, etc. for any contact info for Opus - not sure if they list anything... I don't know how to get online to the manufacturer.
Well, it looks that since your charger is perhaps one of the very few reported to be defective, while I look at it as the minority, you look at your case as perhaps the majority, with most of the ‘typical buyers’, as you term it, not aware that their unit is having the same problem as yours,….
Oh well, it now looks that it depends at which vantage point people look from.
- please don't make implications and assumptions about what I feel behind my words - facts are facts.
One problem with Chinese manufacturing…
A factory can make 10,000 perfect units and the next day make 10,000 defective units.
The problem is, both units will remain in the supply chain for years.
Once a serious defect is discovered in one batch, it is best to just stay away from the model all together.
This is a similar issue when a clone item hits the market that is not distinguishable from the original; best to just avoid the brand.
Tom… no offer for a full refund? PayPal may have something to say about this now that you have a letter from the manufacturer acknowledging a problem.
I discharged a 18650 laptop pull after charging it in slot 1 of my Opus. It was at 4.16v on my DMM but I don’t what it came off at an hour of so prior to looking at it. Below are the numbers for when it was fully charged to 4.20 on my hobby charged and then charged to 4.16 on the Opus
4.20v - 2016 mAh (unknown slot)
4.16v - 1980 mAh (slot 1)
For this cell the 1.8% difference would likely not be noticeable in real life usage for me.
Thanks… that is probably within the margin of error between discharge runs or devices.
The main purpose for going for the Opus is to determine cell health for the cells I use every day. Also to weed out imposters when buying new cells. I trust that the Opus will be accurate enough for that. Also some NiMh compatibility will be welcome.
I just checked 7 assorted LiIon cells between the Opus BT-3100 v2.0, v2.1, Fluke DMM, and UNI-T UT33D DMM (sells for $15 but a good one...). For all 7, the two DMM's read the same exact values to the 1/100th volt. The v2.1 was 0.06v high on all 7 and the v2.0 was 0.03v to 0.04v low. The cells were 2 14500's, 3 18650's and 2 26650's. All cells were in the 4.01v and 4.23v range.
I checked the unit, the box and op instructions of the Opus and there is nothing on the manufacturer - only one place "Opus" is mentioned on the box, one place on the unit. No contact info at all... Typical I suppose but it sure is not like an Xtar, JetBeam, or NiteCore.
Another set of tests:
SONY, pack pull SF US18650GR: 3.05v on DMM's, 3.09v on Opus 2.1, 3.01v on Opus 2.0
Samsung INR 18650 15M: 3.23 on DMM's, 3.27v on Opus 2.1, 3.18v on Opus 2.0
The Opus 2.1 gets closer to the DMM readings for cells at lower voltage levels, while the 2.0 gets further away... In fact the Opus 2.1 is maybe a tad more accurate than the Opus 2.0 at lower voltages.
Again, I don't mean to imply you will see these results typically - mine could be the 1 of 1000 units sold, but it also could be the 1 of 10 units, one bad apple (at least one other reported though), or a bad batch - no telling at this point. Just wish there was a way to reach Henry Xu...
4.15V "FULL" for my v2.1 unit 
. Tested with 5 different batteries from 14500~26650. I thought v2.1 is suppose to be quieter with new fan? Or v2 is even worst than it? I do not think I can charge battery in my bedroom in future ...