Nothing dangerous really.
There will simply be a bit higher power loss going to the phone, making it charge slowler.
It is not dangerous. Voltages above 5.25V may be dangerous, it depends on the phone (I would not expect any danger below 5.5V). High noise levels may interfere with the touch screen and with receiving, but it will depend on the frequency content and level of the noise and how sensitive the phone is for noise. It is not dangerous for the phone.
This looks like an excellent charger/powerbank combination for travelling light. Thanks for the review.
Hi HKJ
Any chance you will disassemble the powerbank to take a look at the internals? Anyone seen the PCB before? No idea why the PB is designed so large with so much space wastage on battery bays (the sides). It could be very much smaller.
What does this mean?
I would want it a bit longer in the bay to accommodate button top cells. And the worst flaw of all is its inability to charge low draw items, ie: Nitecore TIP/TINI/Tube, Sansa/Sony MP3 players, UltraTac K18 mini charger, MecArmy SGN5, and anything drawing less than 300mA.
Not handy at all on a long trip. Why did they limit it so?
UPS is “uninterruptible power supply” and means the device will switch smoothly between input power and battery and back again to always supply output power.
No, I do not want to break it open. The width of the sides are probably to support the magnets.
Okay, I understand what a UPS is. What I don’t understand is where you said it turns off when USB power is removed. Do you mean that it turns off briefly or turns off completely, and something has to be done to turn it back on?
If input to the Xtar drops, then recovers, the Xtar will carry on charging as before, but the output of the Xtar to a connected device will drop, and not resume until the Xtar button is pressed.
Okay, thanks for the explanation Zulumoose! It seems like a weird bug. I hope XTAR fixes it in the future.
2A output is important for me. Can you recommend a similar power bank that has lower noise.
Doesn’t have to be 2 cells. 3, 4 or more cells would be even more great 
The diagram and comments below are an excerpt from the HKJ report above.
Can one infer from this diagram that the efficiency for the PB2 with one cell averages about 88%? Can one also assume that the efficiency will be about the same with two cells?
BTW, the advertised efficiency from the XTAR Official Store on AliExpress is "up to 92%." Thanks.
<START EXCERPT>
Below efficiency curve is only valid with one battery in the charger.
As a power bank it can easily deliver 0.5A until the battery is down to about 3.2V, where it turns off
<END EXCERPT>
Why are there no USB out efficiency measurements available with two cells in the PB2? HKJ, thanks for what you do!
Efficiency will be best with highest input voltage and fairly low current drain (How low depends on the consumption of the circuit itself), I would not expect much if any difference between one and two cells.
The problem measuring efficiency is that I need to measure the battery current, this requires I put something between the battery and the boost converter in the box. I have only made one sensor for this, if I wanted to do it for two batteries I would need two sensors and four voltmeters on the battery side (Or open the box and mount a resistor between batteries and boost converter).
HKJ, thank you for the quick reply - and your good, hard work. Could you make a qualitative assessment of the PB2 power bank USB out efficiency in comparison to others that you have tested? Would you say it Is above average, for example? What do you think of the manufacturer's claim of up to 92% efficiency? Thanks.
The 92% sounds about right, the numbers in my logfile says 91.5% at the start. There is some tolerance on my measurement, the usb cable and connections will add resistance and my 10ohm load resistor is 0.3% too high.
I cannot remember the efficiency of the different power banks I test, you will have to find them and compare the efficiency curve, but it is better than Soshine E4S.
HKJ,
Is it possible that in future tests, you also give a few efficiency percentages at different loads if you happen to know them as ‘byproduct’ of your tests?
You already get efficiency at 3 different currents: 0.5A, 1A and 2A
I do not measure them when doing load sweep, because I do not have sense electronic on the batteries while doing that test.
My problem is that the sense electronic will degrade the performance of the power bank slightly. I do that when running discharge test, but avoid it on the load sweep.
I guess I need a crash course reading your tests
Anyway I checked the graphs again, and see an efficiency line in some graphs.
But I don’t in others.
Xta PB2 usb out 5ohm (2xSA18650-33)
Xta PB2 usb out 2.5ohm (2xSA18650-33)
I see no black efficiency line in those graphs.
Well, I do all the way at the end.
Does that mean the efficiency line is hidden under the USB voltage* line?
*= I think that’s USB voltage instead of (battery) voltage. My ageing eyes have some trouble keeping the reds apart.
If not too much trouble, can you consider more contrasting colors in future tests?
If the efficiencies are what I think the are, the Xtar is very good. Always well above 85%. That’s (almost) on par with Anker stuff.
But that comparison possibly isn’t fair. My reasoning is this, and please correct me if I’m wrong: The Anker likely has 8 cells, 4x more than the Xtar; so at a 2A draw the Anker cells have to deliver 4x less per cell, and that increases efficiency.
HKJ please don’t see the above as talking negative about your work. A little secret… when I’m looking for something the very first thing I do is scroll down to the conclusion of your tests. If it doesn’t get your thumbs up, I don’t even bother reading the rest.
Keep up teh good work buddy!
Efficiency will only be valid with one cell, one the 2xSA18650-33 charts it will be way to high, because I only measure current for one cell.
Number of cells do not really affect efficiency, but each cell may deliver slightly more energy due to less voltage sag.