[Review] XTAR PB2S - Powerbank Charger with 2 Slots, 21700 Capability, QC3.0, USB-C

Budda · 2019-08-28T08:53:48.000Z

I received the XTAR PB2S for the review by XTAR.

The PB2S is a 2 slot battery charger with power bank with power bank functionality QC3.0 (5V 2A or 9V 2A, max power 18W).
The supported batteries are: Li-Ion 3.6 – 3.7 Volt / IMR / INR / ICR; in the 18650-18700-20700 and 21700 format. Protected 18650 will also fit. It can reset triggered PCB circuits of batteries on both slots.
It is available in different colours, I got my sample in black.

I have almost no knowledge about electronic, however, I’ve been using flashlights, batteries and chargers for 10+ years as a consumer. So in this thread I’ll give you my honest opinion on this product as a user.

In order to fully display the potential of the PB2S, along with it I received a Xtar 21700 4200mAh 45A battery, a 18650 2600mAh 35A battery, and a XTAR USB power source rated QC 3.0 .
The PB2S arrives in this nice box with a cut in to view the PB2S. The PB2S comes with a USB-USB type C cable, and a manual.

The PB2S measures 124 mm in length, 56 mm width and 26 mm thick. The entire surface is rubberised and allows a good grip on the PB2S.

On the Front there is the removable tray cover, and the LCD backlit display.

On the back there are the detailed specs (input, output, usb output, batteries compatible…).

The USB output port, the USB-C input port and the switch are placed laterally.

Let’s open the tray by removing the magnetic cover (that works in both ways).

The 2 slots are so long that they can fit long protected 18650 and unprotected 21700 batteries without problems.

Fixed on one side of the charger there is a 11 cm long strap that can be used to extract the batteries effortlessly without tools.

The positive contact point are raised dots (so flat top cells work) and the negative are spring covered by cylinders to provide the maximum contact area.

The display has big digits and being backlit, can be seen in the dark.
The display will show the input voltage, current, and battery capacity percentage.

During my experience with the charger, the it did turn on and off in loop (flashing the information) while being charged and when charging a device. The same when charging the PB2S, even with a QC3.0 power supply. Only once the display stood on, and I could not replicate it.
When the batteries inside are completely discharged, no message appears on the display and you can’t turn it on. You have to charge it to reactivate the display.
Sometimes the display would stay on (flashing the info) even after I disconnected the device I was charging with the PB2S.

Press the lateral switch to cycle between the average value (IN), and the value of each battery (B1 and B2).
The Display will show:
IN when charging,
OUT1 or OUT2 when discharging
%: power percentage of the batteries (if one battery is inserted it shows the percentage of the single cell, if two batteries are inserted, it shows the average percentage of both cells).
ER: error (battery wrongly inserted, or battery defected / not recognised).

As far as the input, the PB2S works with QC3.0 (5V 2A,9V 2A), and it can charge the inserted cells at 2A on each slot (2Ax2), 2A on one slot (2Ax1) or 1A on 2 slot (1Ax2).

When the cells inserted have different voltage, when charging (or discharging), the PB2S will start charging (or discharging) the one with the higher voltage, when they have the same voltage, they will be charged (or discharged) both at the same time.

If you want to keep the PB2S connected to a device but stop his output as a powerbank, just keep pressed the lateral button until the displays turns and stays off.

Here is the speed reading on my phone when charging it with the PB2S

And here is a thermal pic of the phone being charged by the PB2S.

Here is a video of the PB2S being charged with the XTAR USB power supply with QC 3.0 (speed 16x)

My thoughts
The PB2S is well built and finished.
The magnetic tray cover works well staying in place protecting the tray and the cells from dust and accidental contacts when carrying the PB2S. The 2 slots are long enough to accommodate most cells.
The USB C / USB ports are universal and allow more current than the micro USB port, allowing for the fastest charge.
Charging the PB2S using a QC3.0 coded power adapter, a Ravpower Smart+ 2.0 charger, and other regular USB chargers without particular coding or rating, I had no problems.
Using the PB2S as a powerbank to charge my cellphone, and other equipment, worked fine even with a single cell.
The possibility to run the PB2S with different sizes of batteries, from the 18650 to the 21700 with 2 independent slots are a plus. Although I would advise a word of caution when putting in smaller cells that for capacity and or chemistry, can not support the 2A charge that could be delivered to them. Similarly, I would advise caution when powering the powerbank function with a single cell that for capacity and or chemistry, can not support the high continuous current discharge.
In my opinion, you can fully exploit the technical advantages of the PB2S if you run it with IMR or hybrid cells, so you can use the fast charging currents to fast charge them, and they can take the high and prolongated discharge current to sustain the highest charging current that the PB2S is able to sustain, especially when running the PB2S with a single cell.
Using quality USB C cable (with the right coding) is also a must, to avoid additional bottlenecks that can diminish the overall performance of the PB2S.

Keep in mind that. Although the % indicated for the single battery is a more or less accurate indication of the capacity remaining for that battery, the average % could not reflect the real capacity remaining in the PB2S if you use 2 batteries with different capacity, because the % estimate is done measuring the voltage of the cell.
For example, carrying an almost empty (10) 2000mAh 18650 cell, and a full (100) 4200mAh 21700 battery, will give you an average remaining capacity of around 55, when in reality you have around 70.
The other way around: a fully charged 2000mAh 18650 and a almost empty 4200mah 21700 will give you the same average remaining capacity of 55, when in reality you have around 40.
This issue can be minimised or nullified if the batteries used in the PB2S have small to none difference in capacity.

The only issue that I have with the PB2S is that when the display doesn’t stay on constantly, but it turns on and off, and stays on every time for around 1 second. That is not enough for me to grasp all the informations (current, voltage, %) in a single cycle, I have to wait for the display to turn on again to read the rest of the informations. Same for the display remaining active, flashing, even when I disconnect the device I was charging.

Thanks to: AntoLed, Won, Zampa.

maukka · 2019-08-28T10:04:31.000Z

Thanks for the test!

How’s the efficiency? How many Wh do you get out of it with a couple 3000mAh / 11Wh 18650s say at 2A/5V output? And reverse, how many Wh does the charger consume if you fully charge those back up?

Budda · 2019-08-28T10:11:41.000Z

Hi Maukka,
unfortunately I have no time to measure the efficiency. I even tried to see how many times I could charge my phone but then I realised that the phone was always at a different charge, and sometimes with GPS, bluetooth and screen on, and sometimes it was just in standby. So, no real consistence in this test.
Do you have any advice?

maukka · 2019-08-28T11:15:49.000Z

Just a basic USB inline meter that logs watt-hours would do the job.

Does it work well with a USB solar panel charger? I mean does it reset and start again if input voltage and current suddenly drop dramatically.

Budda · 2019-08-28T12:16:30.000Z

do you have any products to suggest for me to get to obtain this measure?

Blggg · 2019-09-28T04:23:57.000Z

Hi maukka,

Hope it’s not too late to give you some of the readings I’ve got.

Disclaimer: I only discharged the 21700 batteries into my Nokia 7 plus, which has 3,800 mAh of battery capacity, so it can fully discharge only one 21700 battery. The readings are from a usb tester.

With 1*21700 battery,
I fully discharged a Samsung 40T and managed to get around 73-74% of efficiency. The average discharge rate is 5V/1.5A, and the charge back rate is 5V/2A.

With 2*21700 batteries,
When partially discharging two cells (unfortunately I don’t have a tablet or something that can empty 2*21700s). I managed to get around 73-75% of efficiency. The average discharge rate is 5V/2.5A, and the charge back rate is 9V/2A.

However, under the same scenario, when charging the cells back using 12V (I always get 12V when charging 2 cells with my Nokia 7 plus adapter, which has the same spec as the ZMI dual port QC3 wall adapter (5V/3A, 9V/2A, 12V/1.5A), which will only charge 2 cells at 9V max, never goes up to 12V). I managed to get 80% of efficiency.

What do you think? To me, a high charge voltage seems to play huge part in the efficiency.

Note: The efficiency would have been a bit better I think, if we can lower the discharge rate.

maukka · 2019-09-28T08:26:17.000Z

Thanks. That boost charger efficiency seems quite low while the buck in the input is marginally better.

Blggg · 2019-09-28T09:26:21.000Z

Sorry, maukka. I’m a noob. Does it mean it’s good or not? Sounds like the charger is not up to your expectation, right? I supposed. If we charge the batteries back at 1A, we will get the efficiency of about 73-75%, so I guess that’s its kind of norminal efficiency. Charging back at 12V seems a bit unnatural to me.

However, compared to the Nitecore F2, efficiency-wise, the PB2S does quite an excellent job. I got just about 56% out of the F2 (from 1*21700). Not sure if something was wrong with my test. But almost 20% difference is insane.

fluke · 2019-11-06T13:48:53.000Z

Does anyone know if the double press low mode has a timer

maukka · 2019-11-06T13:51:03.000Z

No timer.

fluke · 2019-11-06T13:53:22.000Z

Thank you.

Bluecharge · 2020-01-17T17:27:33.000Z

“The only issue that I have with the PB2S is that when the display doesn’t stay on constantly, but it turns on and off, and stays on every time for around 1 second. That is not enough for me to grasp all the informations (current, voltage, %) in a single cycle, I have to wait for the display to turn on again to read the rest of the informations. Same for the display remaining active, flashing, even when I disconnect the device I was charging.”

Well this really is a major issue and for me its a dealbreaker.
Not only the display doesn´t stay on, but the whole device cycles constantly on - off - on -off. This means, it won´t charge your phone or whatever would like to take a bit more charging power.

This issue happens if the batteries in the PB2S are partedly depleated (20% - 30% both) and you try to use this little rest to charge your phone, perhaps because you are in need of energy and happen to have no other source.

A decent powerbank of course will charge your phone until it´s depleated to 0%.
The XTAR PB2S can´t do, because of this on - off cycling.
Whats the point in the PB2S with its dedicated powerbank function, if it can´t use the full capacity of the inserted batteries? For me it´s useless. I wonder, how anybody can be satisfied with that.

I regret that many superficial reviews on youtube and on other platforms doesn´t notice this issue. This is sad for all the good faithed customers…

Petr_J · 2020-01-17T22:18:38.000Z

So far, I have discharged PB2S to at least about 44%. I did not notice the display flashing. Tomorrow I will test the discharge for lower residual capacity.

Petr_J · 2020-01-20T20:50:27.000Z

Today I tested the charger until it discharged to 10% capacity. The display does not flash. Do you have the low charging current mode on? In this mode, the display flashes.

Blggg · 2020-02-01T12:36:19.000Z

Petr J.:

Today I tested the charger until it discharged to 10% capacity. The display does not flash. Do you have the low charging current mode on? In this mode, the display flashes.

If I don’t misremember, mine also flashes as well, but not every time though. Have you tried measuring the actual voltage left instead of the battery percentage shown on the display? I suspect that there might be a hugh inconsistency between the actual voltage and the battery percentage shown. I think actually the charger discharges the 18650 (only one inserted) to about somewhere between 3.1-3.3 volts, which isn’t so bad but could be lower though. But the percentage on the display still shows something like 10-30% which makes us think that the charger has turned off too soon.