XTAR is a maker of many, and fast chargers.  They have a new on on the market!  It’s an update to the poorly named “Over 4 Slim.”  This one’s been updated to USB-C, and is called the ST2.

Official Specs and Features

Here’s a link to the official product page.


This charger is going for around $40 at the moment.

Short Review

The ST2 seems to meet specification, and also runs on USB-C.  That’s a nice update.  It does charge at over 4A, so if that’s a feature you need, this charger is one option to get it.

Long Review

Key Features

• 30min Fully Charged
• 4.1A Ultra-fast Charging for Two Slots
• Type-C Port, Dual Fast Charging Protocol
• Automatically Test Resistance, Select the Best Charging Strategy
• Compatible with 21700/26650 Li-ion Batteries
• Intelligent Temperature Control Sensing System
• Delicate Design, Skin-friendly Touch
• Manual & Auto, Flexible Control
• Easy Operation, Clear Display
• Small & Portable, Grip by One Hand

Manual and Packaging

I didn’t actually get any packaging with my ST2, so I’m not sure what the retail package looks like.

I also didn’t get a manual.

What’s Included

Again, I didn’t get a retail package.  But with my ST2, I got the items above.

  • XTAR ST2 2-bay charger
  • USB to USB-C cable
  • USB-C to USB-C cable
  • XTAR Wall Adapter

Build Quality and Durability

This is a well built charger.  There’s a grippy surface that seems to add to the quality feel (instead of detract from it, as you might expect).

The front of the ST2 has a little foot (which is not also a screw cover, whereas al the other feet are screw hole covers).  This foot on the front is very useful – it supports the charger from flipping up when the buttons are pressed.  The USB-C port on the back is also perfectly fit into the case.

Here’s a bit of a teardown.  I don’t suppose I tore it fully apart, but you can see the goodies.

Note those two sets of  very thin wires – those are for the temperature sensors in each bay.


Officially the dimensions are 149mm long, 75mm wide, and 33mm high.

Moderate size for a 2-bay charger, but it does support wide cells.  The bays won’t really handle shorter than 18650, but they’ll go all the way up to 21700 in length.


The ST2 needs a USB-C plug, but it’ll work off USB-C to USB-C, or USB to USB-C.  Either’s fine, but USB-C to USB-C is likely better, since the charger supports PD2 charging.

XTAR provided a solid wall wart for this review.  I won’t review it separately, but I do recommend it.

It’s USB-C, obviously.

When I pulled it out of the package, and saw the item below, I disappointedly thought I had the wrong location adapter.

But I was wrong, and check this out.  How clever is the adapter!!

As for what the ST2 can power – as I said above it’s basically anything the length of 18650 minimum, and 21700 max.  Diameter (as seen below) is fine with 26650 cells.  Li-ion only too; no NiMH.

User Interface and Operation

There are two buttons on the ST2.  Each bay has one, and they’re right at the bottom.  They’re squishy and clicky enough, and pleasantly quiet.

Upon power up, the charger LCD lights bright blue, and the default charge current (2A) is displayed.  When a cell is dropped in, the LCD directly under the bay being used displays the charged percentage, cell voltage, cell temp, and charge current.

Holding the button (either button) will turn the back light off (something you’ll probably want to do; it’s bright).  Any further click bring it back bright.

When the charger is on (whether a cell is in place or not), button presses select the charge current.  If a cell’s internal resistance is too high, 4.1A will not be an option.  Internal resistance is shown just after a cell is inserted into a bay.

There is a bit of a weird thing that when charging USB-C to USB-C, the ST2 doesn’t like for cells to be in place when power is applied to the device.  Basically it’s required to power the device first, then place the cells into the bays.  Not the end of the world.

I performed some charge tests, which mainly just point to whether the charger does what it claims to.  It does charge at 4.1A, and it’ll do so with one or both bays filled.  I do note that in one test at the high current below, the current switched down to ~3A – that’s likely due to temperature (but I don’t log temp, so I can’t say for certain.)

This (above) is the only real anomalous result.  It seems that after I’ve manually selected 1A charge current with 1 cell in the charger, it bumps up to 2A if the situation is right.  Ie if the IR is low enough, and the temp is low enough.  This isn’t my preferred behavior, but it could be worse.

The ST2 does charge at 4.1A.  There’s not much more to say than that.  It’s a user friendly charger, great for fast charging.


What I like

  • Nice design
  • USB-C update
  • Real 4.1A charging
  • Real 4.1A charging even on both bays at once
  • Nice temperature monitoring

What I don’t like

  • Seems to pick a higher current if a cells IR supports it
  • Weirdness with USB-C to USB-C and powering at startup
  • Throwing a USB-out on this would be pretty fantastic.


  • This item was provided by XTAR for review.  I was not paid to write this review.
  • This content originally appeared at zeroair.org.  Please visit there for the best experience!
  • Whether or not I have a coupon for this charger, I do have a bunch of coupons!!  Have a look at my spreadsheet for BangGood and GearBest coupons. Please subscribe and get notifications when the sheet is edited!!

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