Xtar PB2S 2 cell Li-ion quick charger

Full disclosure: I received this Xtar PB2S charger free of charge (ba-dum-tsss) for the purpose of reviewing it. Other than the free charger, I am not getting paid for this.

As I’m not relying on writing reviews for my income, or even for free stuff, I will give you my honest opinion about the product, regardless of what the manufacturer feels about that.

First impressions

The MSRP for the Xtar PB2S is $21.90. You can find the official specs for this charger at the official Xtar site.

Big fish, little fish, cardboard box

I’m not one of those reviewers who care a lot about the presentation, and since this is not a typical gift, I’m glad Xtar didn’t spend too much money on the packaging.

The packaging

The box is fine, it holds the product. It’s nice to see that it’s one piece of plastic and one piece of cardboard, though. Easily separatable and recyclable.

But the main thing here is what is inside.

What you get in the box

What you see is what you get

In addition to the charger itself, there’s a 76 cm (about 30 inches) long Xtar branded USB-C cable which seems to be of decent quality, and a user manual in eleven languages.

User manual in English

Here is a scan of the English version. Click the thumbnail to have a closer look.

The Xtar PB2S itself

Not a bad looking device

The Xtar PB2S itself certainly looks better than the four bay Xtar VC4 that has been my daily charger for a few years now. (I should probably write a long term review of the VC4 as well. I will link it here if I ever get around to it.)

I got the blue one, but there’s also a yellow, a red and a black version.

Detachable magnetic lid. Spring loaded negative poles. A flappy floppy band to free the cells.

The two studs on the negative end of the battery are spring loaded. You can fit 18650, 18700, 20700 and 21700 batteries in it, according to Xtar. You won’t have any luck with 18500 or shorter batteries, the studs are too short for that.

There are two magnets on the cover. The band is practical for getting the batteries out.

Although the screen is slightly blurry from the textured semi-transparent plastic,
this picture doesn’t really do it justice. It is a bit better than this.

The screen is reasonably bright and clear, and shows battery percentage, voltage, and current. In addition, there’s an indicator that tells you whether it’s charging (IN) or discharging (OUT1/OUT2) the batteries.

The USB-C port is usable for both input and output. The USB-A port is for output only.

Charging and discharging

I tried it with an Aukey battery bank that supports Quick Charge, and I was able to get it into QC3 mode both when changing through the USB-C port and when dischanging through the USB-A port.

Single battery discharging

I connected a multimeter directly to a single, nearly empty, 18650, to measure the cell voltage. I then tried to charge my phone from the Xtar.

The phone didn’t want to quick charge, possibly because of the single cell with little charge in it. Reasonable enough.

I watched the voltage on my multimeter decrease as the Xtar (according to its display) kept pushing 1A out of its USB-A port at 4.9V. At a cell voltage of 2.8V the Xtar cut off, which seems like a good place to have the discharge voltage limit. Curiously it was still showing 42% capacity.

Single battery changing

After I had drained the battery to 2.8V, I immediately connected the Xtar to a QC3 capable power bank, in order to charge the 18650 back up.

A simple charge test setup

Here I ran into a little snag. The Xtar did not seem to approve of being switched from battery bank mode to charger mode in such short order.

It did seem to charge the cell, but the display kept blinking off and on. When I disconnected the battery bank, pulled the cell out of the Xtar, and put it back in, everything went back to normal.

Now the cell voltage was climbing steadily, while the Xtar showed that it received 1.8A at 4.9V through its USB-C port. I’m not sure why it didn’t request a higher voltage from the QC power bank; Perhaps it is more efficient to ask for the lowest voltage possible, since that would still be higher than the max voltage of the single cell.

  • At a cell voltage of 4.1V the Xtar PB2S was only showing 55%.
  • 4.125V: The Xtar dropped from 1.8A to 1.7A, showing 57%.
  • 4.13V: It was clearly in the CV region of its charging algorithm, as the current started dropping more rapidly.
  • 4.16V: 0.8A and 67% capacity.
  • 4.18V: 0.1A and 82%.
  • 4.19V: 0.1A and 90%.
  • 4.195V: 0.1A and 92%.
  • 4.2V: It stopped changing and showed 100% capacity.

Internals

This unit seems to be well put together. In fact I could not find a non-descructive way to disassemble it.

I don’t know if Xtar glued it, ultrasonically welded it or what, but there was hardly any flex or creaking when I tried to apply force to it. I also tried to separate the shell using a sharp implement, but I stopped before I stabbed my hand.

Shedding some light on the internals

I could measure continuity between the negative poles though, and shining some light through the box seems to confirm that these are commoned together. No series charging or discharging, in other words.

There’s no circuitry in the middle part of the enclosure, other than the wire going between the bottom with the negative terminals, and the control circuit under the display.

Xtar PB2S closing thoughts

My first impression is that the Xtar PB2S seems to be a solid product in a nice form factor. The user interface is simple and although I ran into a single glitch, only time will tell if it was a one time event or something more. The MSRP also seems reasonable to me, for what this is and what it can do.

Don’t use this charger with batteries that can’t take a 2A charging current though. There’s no way to limit the charging current, so you better make sure your cells can handle it at full blast.

I suspect that crushing the device to see what’s inside would reveal no more than a QC chip, a boost converter, a few MOSFETs, a microcontroller and some passives. There is probably not much I can glean from the circuit itself, and certaintly nothing that I would care to reverse engineer.

Instead, I will now put this charger in service, and see how it fares in everyday use. If and when I get more experience with it, I may do some more measurements, and perhaps write a follow-up.

Second impressions

After a few days of use, here are some notes:

  • You can press the button while charging, to see the cell voltage, current and “capacity percentage” for each individual cell.
  • The one feature that I miss from my VC4 is the ability to see how many mAh has been delivered to the cell. The “capacity percentage” number is not very useful to me. I look at the cell voltage instead. I guess there’s only so much you can do with the limited screen real estate of a compact charger.
  • When I take out fully charged batteries and insert empty batteries, the display sometimes freaks out and starts flashing. Whenever this has happened, I have completely rebooted the PB2S, and that has fixed it. Perhaps it would have fixed itself after a while if I just left it alone. I haven’t tried that yet.
  • The displayed values for the individual cells don’t always make sense. For example, when charging two cells at the same time, at one point cell 1 showed more than 3A (the charger is rated as max 2A per cell) while cell 2 showed 0A (but still seemed to be charging). This does not inspire confidence.

I don’t yet know if the display problems are limited to the display, or if they affect the actual charging of the cells. Hopefully it’s just the display: If the charging is buggy, that can be a serious issue. I will have to look into that.

My thoughts for now is that it’s a bit disappointing that a well designed, well built and generally well thought out product like this would be hampered by buggy firmware or electronic problems. I hope this is something Xtar can and will fix as soon as possible, before this model gets a bad reputation.

Third impressions

After having used the charger for almost two months, I am ready to give you my final thoughts.

The PB2S has been charging my batteries just fine, and it has been reliable and useful. It doesn’t get hot. It stops at 4.2V like it’s supposed to. I have brought it with me traveling, and I trust it enough that I have not felt the need to bring a backup.

The USB3 port and QuickCharge capabilities makes it a versatile and powerful charger. The physical design and construction is top notch in my opinion.

However, the display is neither precise nor accurate. When inserting a battery, the readings take a while to settle to a sensible value. Even then, the voltage readings are easily off by 0.1V and the current by 100 mA.

In my opinion, an inaccurate reading is no better than no reading at all. If the charger had simply used a red, a yellow and a green LEDs to display the status for each cell, instead of the over-complicated and under-performing numeric display, that would have been just as informative and useful.

It would also have made the charger easier to use, and it would have inspired more confidence than a flaky readout that may or may not be correct at any given moment.

So my final verdict is that this is a nice little charger that I can actually recommend, despite it unfortunately being let down by a display that is, in my personal opinion, pretty much useless.

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