Test/review of Xtar PB2 Charger & power bank

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 :slight_smile:

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.


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


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.


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 :slight_smile:
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.

For me that’s the main measurement of efficiency.
The percentage of energy in the cell(s) that becomes available at the USB port of the power bank.

It is not called efficiency and you can find data for that in my battery test.

Then I simply don’t understand it.
If the battery outputs 3500 mAh and the power bank’s electronics only outputs 3000 mAh, I can the difference (lack of) efficiency, because 500 mAh was turned into useless heat.
I don’t see how a batterytest is relevant to this.

Anyway, thanks for the test, I ordered the Xtar.

Lower current draw from a battery will get more energy from the battery, that has nothing to do with the boost converter in the power bank, but depends on the battery chemistry.
Boosting the resulting battery voltage to 5V is the job of the boost converter and there the efficiency is interesting.

Both parameters will affect the final amount of energy you can get from the power bank.

When looking at efficiency and you have different voltage, you need to do the calculations in watt or Wh, not mA or mAh.

Sure I understand what the cell delivers can, and does, also suffer from inefficiencies. Really I’m not questioning that at all.

Perhaps I should have made myself more clear. The 3500 mAh I mentioned was net power coming from the cell. That’s +after+ all the losses in the battery.

So what I’m after is only the losses of the Xtar electronics.
Afteral it’s not fair to blame very bad performance of a cell on the Xstar.
Just like it’s not fair to blame losses due to a bad quality 10ft long cable between charger and phone.
Those are all different products and while they for sure have a combined efficiency, you can’t blame Xstar for that.


I used the XTAR PB2 in the last 2 days to charge my smartphone .

I put 2 Sony VTC6 (+/- 3000mAh) on it and I managed to make 2 charges, even if they were not full: initial “load”, as shown in the PB2, was 88%, batteries were about 4.13V each.

Today I used it and it went back to 0% load, batteries were at 3.08V.

Later today: I put the batteries charging in the PB2. They were at 3.08V on the beginning. About 5 hours later, more or less, they were fully charged up to 4.20V (confirmed on the Opus BT-C3100).
Don’t know if this is important or not, but it is some “data”!

XTAR is teasing it's new PB2S on Instragram and it looks pretty promising. From the video:

  • QC3.0 in/out (9V 2A max)
  • USB-A out, USB-C in (probably not to spec)
  • 18650 up to 21700 cells supported
  • In/out current and voltage display

Nice to seee addition of USB-C and support for longer cells - if that USB-C actually works to charge modern devices with a C-C cable, I'll pick one of these up so fast. If it doesn't... Meh. Still some nice upgrades from the original.

Anyone else having problems with their PB2 not outputting more than about 1A? It takes hours to charge my phone with it because of this and it’s not worth using when it’s that slow.

I’m not completely sure, but it’s possible your phone is controlling the charge rate and not allowing a full 2A charge.