[Review]Xtar ST2 Battery Charger (USB-C Input, Selectable Speed, Dual slot 4.1A Each)

liquidretro · 2019-07-21T21:15:16.000Z

I am no HJK but here is my take on the new Xtar ST2.

Xtar has introduced their new 2 bay lithium ion based charger and it’s capable of charging 2 cells at 4.1A each from USB-C! It features selectable charging rates too. Thanks to Xtar from sending me this early unit for a quick look and review along with a few high drain batteries to test with.

Full Image Gallery: https://imgur.com/a/CfM55vl
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Packaging
The charger I received was early in the production cycle and didn’t actually come with any of the final retail packaging. The accessories that will be included with the final product are the charger itself, USB-C to C cable, and a USB-A to USB-C cable thats QC3 compliant.

Construction
This charger is designed to charge cells 18650 and larger, primarily 18650, 18700, 20700, 21700, and 26650 batteries. To accomplish this Xtar made a few design changes. Instead of the positive end of the batteries facing the power plug, now the positive end faces the screen which is 180 degrees from pretty much all other chargers. Thankfully this is molded into the fire resistant plastic. They also designed the sliders (at the top) so no smaller batteries will fit, 18650’s are the minimum size. This charger should also charge protected 21700’s. Minimum size the charger accepts is 60mm, and maximum is 77mm. The charge now has temperature sensors on each bay in little metal pads that make direct contact with the batteries.

The sides pick up the blue theme with accents and the entire thing is made of soft touch flame retardant plastic. There are vents on the back and bottom of the charger to aid in cooling. Overall it’s made pretty well and feels solid.

As noted before the screen on this charger is on the bottom of it, and while the screen part itself is fairly small. Text is large enough and very clear. The background is a nice deep blue and text is white. The display shows the current voltage of the cell, Percentage of charge, charging speed, and temperature of the cell in centigrade. When you first plug in the charger it will do a test and show the resistance of the cell.

Below the screen you do have two buttons for each charging slot. These control the charging speed of each slot, with your options being 1A, 2A, or 4.1A. If you hold the button for 1.5 seconds the backlight and LED will turn completely off for night charging, although the red and green LED indicators (Charging/Charged) will stay on. The backlight will go to sleep after a few second under normal operation.

Here are some photos of the interior of the charger. My only concern is that the wires to the temperature sensor are very thin and I could see these potentially getting caught in the spring or mechanism.

Rather then read out the input and output specs I will throw a picture in here.

Charging via QC3
When charging via QC3, the charger is not capable of charging 2 batteries at 4.1A each. Instead it will charge 2 batteries at a maximum of 2A each. If you drop down to one cell it will charge at 4.1A. There is no indicator on the screen what your power source is, if it’s QC2 or QC3.

Charging via USB-C!
For maximum performance across both bays, the best thing is to use a power supply that capable of at least 40W (measured at the wall) or more via USB-C PD. I used my Innergie 60C charger for my testing because it’s the only USB-C charger I have that could deliver enough power. I tried my Xtar EU4 with USB-C but when loading up 2 batteries it would shut off when I tried to charge both at 4.1A.

When charging 2x 21700 batteries at 4.1A each at the start the charger was drawing 40W @ 0.74A at the wall. The cells started off at 24C. At 7% charger they had heated up to 30C. At 25% charge they were 45C and this was as hot as the charger reported things as getting, and my infrared thermometer measured similar temps. Total time to charge both 4000mAh 31700 batteries from 3.5V to 4.2 was 1 hour 25 minutes. Terminating voltage was 4.188V

When charging both cells at 2A, I measured a total of 22W of power at the wall, and when charging both at 1A I measured 12W at the wall. These lesser power modes could easily allow you to charge off lesser capable power supplies or using QC3.

Pro’s

USB-C PD! Finally we have a charger utilizing USB-C and PD. QC3 is also an option with a A to C cable.

Speed, this is one of the fastest chargers on the market, able to charge at 4.1A on each bay simultaneously. Great for those high capacity 21700’s and 26650’s if you need the speed.

Selectable Charger Rate, this is something we need from Xtar’s other chargers such as the X and VC series chargers.

Direct and continuous measurement of the temp of the battery, great for safety when charging at such high rates.

Con’s

When using USB-C you must plug the charger in first then insert the batteries.

Cell orientation is backwards from most other chargers with positive terminal facing the user.

Unit shuts off when not receiving enough power (USB-C) instead of charging slower or giving a warning. This is kind of frustrating sometimes.

Larger Lithium batteries only, Unfortunately this isn’t a perfect one stop charger because it doesn’t support Ni-HM cells or smaller Lithium ion like 18350 or 14500.

Conclusion
It’s nice to see a charger finally use USB-C PD and have a battery charger from Xtar that allows you to change the speed of the charge too. The ST2 look a lot like the Xtar Over Slim 4 and has similar specs but with a USB-C input and no USB outputs.

To take advantage of the speed of this charger you really need to use USB-C power supply, and it needs to have a fairly large power output. My Xtar EU4 can put out about 45W on USB-C but that wasn’t enough to charge both cells at 4.1A and the charger shut off, and only my 60W charger was enough.

That said, in most applications I don’t recommend charging your larger batteries at 4.1A each, while it’s safe it does heat them up and causes some unnecessary wear and tear, and shortens they life by a small amount. This would be good for a quick top up if speed was necessary or maybe a boost early on in the charging and then turn down the speed as you go. This fast of charging should only be done on high drain batteries. So at 2A charging this charger needs a much less demanding power supply and this is where QC3 or a more modest USB-C charger comes into play.

This is a good charger for those looking for full USB-C support and outright charging performance in a small package and don’t mind not being able to charge smaller then 18650 lithium batteries or Ni-HM cells.

ZoomieFan · 2019-11-05T09:25:01.000Z

Nice review with some extra information. It’s a very fast charger but I wonder if it could be even faster.
If I look at the graphs in this review I wonder why the current drop is always so close to 60 minutes? Coincidence?

Why such a sharp drop after that hour?
The last graph is even stranger; at about 37mins the amps drop from 4 to 3. But the previous graphs show that throtteling down the amps starts at the 60min mark.

Is it expected that this behavior will be corrected with a firmware update?