May not necessary be fault of the charger, you may as well have too low input voltage or old cells with high resistance.
One MP1 and ML-102 ends at 4,17V, one ML-102 at 4,21V, one MP1 at 4,22V. These two chargers at 4,09V and 4,13V.
Same cell and same USB power adapter.
TP4056 specification is 4,137V-4,263V
That sounds horrible. Mine is not in yet... :( After 30 days today.
They will send me one replacement unit. I hope these one will be ok.
I found the problem.
Charge termination is at C/10. At 1A charge current is termination at 100mA.
But specification 4.137V-4.263V is for 40mA termination current(0,4A charge current). So at 1A charge current you can end even below 4,1V
My bad charger stops at 4,09V if I charge with 1A. But if a change resistor and charge with 0,5A current, it terminate at 4,13V
That is wrong. If you measure the battery voltage even 1 second after the charge is terminated, it is not the charge termination voltage you are measuring.
At lower charge current you will fill more current into the battery and the voltage drop after charge termination will be less. I.e. you will measure higher voltage when charging with lower current and you first measure when the charing is stopped. This is only valid for the same battery, the voltage drop will vary between different batteries.
Today received another two.
One charge till 4,15V, other till 4,17V
How are you measuring?
The only sample I have is at 4.20V and still charging (but not increasing voltage so far).
Here is a teaser, I’ll post a separate article with more pics of my build.
The 0.01V difference visible on the voltmeter is lost in the very thin leads to the cell holder. I’ll upgrade those wires soon, this is a test charge, initial, prototype build.
I’ll post more info as it becomes available.
Viktor
@ all you guys contributing to this thread: ROCK ON! AWESOME! 8)
I have an idea why you are getting so low termination voltages.
This charger module loads with bad (or nonexistent?) CC-CV curve. Once the power supply cable is removed, cell voltage drops a whole 0.1V.
I’ll post results with precise numbers after the blue light turns on.
Mine is at 4.23V at the moment. :~
Viktor
I measure when I take battery of charger. I test with two different voltmeters.
Mine terminated at 4.25V.
At the moment blue diode lit up voltage dropped to 4.23V -> 4.22V … etc. That means there is no trickle charge, or it trickle charges with different voltage (which would be even stranger).
Now, this was a budget, low quality cell. After two hours of resting it dropped to 4.17V. I’ve disconnected both the cell and the USB cable and measured every once in a while.
30 seconds after termination
left: unplugged USB cable 1 minute after termination; right: 20 minutes after termination
Cell was removed from the holder during resting as to not have it drained by the voltmeter.
I’ll be testing this charger more in the next few days and will post more results.
Viktor
as you can see, the charger has a voltmeter. for our purposes it can charge 18650, RCR123, and CR2. 10440 and 14500 are not supported.
it's a new German company. i only trust electronics made in Taiwan Japan Corea. China good too. Germany more good for wurst, beer, bread, cake and cars. haha
ha
I like!
Today I received another two chargers(they resend me after complaint)
4,15V and 4,20V. Much better 
At least one out of four works as described..^^
I have installed one for my XTAR MP1 some months ago, here I add some pics:
Your final voltage will be influenced by many factors, not just the charger.
Same battery, same battery holder, same USB power adapter, same DMM,…
So?
I ordered one of these voltmeters, too. But what's the plug called like? I want to attach testing leads.