The XTAR Visible Mixer VX4 Charger is the first charger that can charge both 1.5V and standard 3.6V/3.7V Li-ion batteries, as well as NiMH and LiFePO4 batteries. This review takes a look at this 4-bay analyzing charger's features and ease of use.
Disclaimer
XTAR send me the VX4 charger for an honest review. The product link is an affiliate link.
Features
The VX4 is a big step up in functionality compared to the popular VC series of chargers. Functionality includes:
4 battery bays.
Real time charging display including voltage, current, and charged capacity (except for 1.5V Li-ion due to how they work).
3Ax1/2Ax2/1Ax4/0.5Ax4/0.25Ax4 charging currents.
Automated charging current (based on power input, number of batteries, and internal resistance).
Low voltage battery recovery.
TC-CC-CV charging for Li-ion.
Multiple protection technologies.
USB-C charging (20W PD recommended, 5V 2A or QC3.0 with performance limitations).
Capacity testing / grading (on discharge) for all battery types.
Dimensions of the VX4 are 172mm x 130mm x 41.5mm, with a weight of 315g. The charger "kit" includes the charger, USB-C to USB-C charging cable, and manual. The charger "set" additionally includes a PD20W adapter. The retail price for the "kit" option was US$45 at the time of writing. There is a 2 year free repair warranty (shipping costs incurred to user), and lifetime technical support.
Battery Compatibility
The XTAR VX4 has impressive cylindrical battery compatibility.
The VX4 is compatible with standard 3.6/3.7V Li-ion (4.2V max) or 3.2V LiFePO4 (3.65V max) batteries in the following sizes - 10440, 14500, 14650, 16340, 17335, 17500, 17670, 18350, 18490, 18500, 18650, 18700, 20700, 21700, 22650, 25500, 26650, and 32650. Unofficially, 26800s should also just fit, though I don't have any to test. The springs have less tension than many other chargers I've used, and the slots are also relatively wide. This makes it easier to insert and remove longer or wider batteries.
The VX4 is also compatible with 1.5V Li-ion in AAA and AA size, and 1.2V NiMH batteries in AAA, AA, A, SC, C, and D sizes. The compatibility with 1.5V Li-ion is a big bonus. It removes the requirement to purchase a dedicated charger for these contemporary battery types that are useful in devices that don't work well with NiMH batteries, such as kids toys with motors, wireless keyboards, or air conditioning remotes with LCD displays. As far as I'm aware, only XTAR 1.5V Li-ion batteries are compatible with the VX4. XTAR kindly send me a few 1.5V Li-ion batteries with the charger to try out.
The VX4 can charge different chemistries at the same time, and at the same charging current, however 3.6V/3.7V Li-ion and 3.2V LiFePO4 batteries cannot be charged simultaneously. A C/V button press required to change between standard (3.6/3.7V Li-ion) and LiFePO4 modes.
There is no compatibility with 3.8V (max 4.35V) Li-ion batteries, however these are rarely used, and I don't see this is an issue. It also reduces the risk of users over charging a 3.6/3.7V Li-ion battery to 4.35V - unfortunately, I've known a couple of people do that.
Charging and Capacity Testing (Grading)
3Ax1, 2Ax2, 1Ax4, 0.5Ax4, and 0.25Ax4 charging currents are available. This is OK, and expected for the price point, but there are a few chargers such as the Vapcell S4 V3.0 that can charge at more than 1A when all 4 bays are in use. By default, the charger automatically chooses the current based on type of battery, number of slots in use, power supply, and internal resistance. Unfortunately the charger doesn't display the internal resistance measurement, and that is in my opinion this charger's biggest omission. The charging current can be manually selected, to choose a lower current than automatically selected - this will apply for all slots. When only one 21700 with low internal resistance was inserted, the charger used 3A charging current by default. When I inserted an older 18650 with very high internal resistance (due to a past over-discharge), the charger soft started at a very low charging current, and after a few minutes raised, but limited charging current to 0.5mA. NiMH is limited to charging at 0.5A. This is fine for AAA, but I prefer to charge FDK made AAs such as Panasonic Eneloops and Ikea Laddas at 1A.
The voltage readings were tested to be accurate within +/- 0.01V. Charge termination also appeared to work correctly for all tested battery types. 3.6/3.7V Li-ion terminated at 4.20V, with CC/CV termination. 1.5V Li-ion is charged using 5V, with the internal battery circuitry terminating the charge when the battery is full, which the charger then responds to.
NiMH battery charging starts with a lower current for the first few minutes. They appear to terminate charge using-dv/dt termination, as there is a rise in voltage shortly before charge terminates. This termination usually occurs at between 1.5V to 1.52V. In one instance I experienced a previously stored NiMH AA battery terminate charge at 1.43V when "topping up". This battery charged correctly on a subsequent attempt, and I think this issue may have been battery related. Sometimes AAA batteries need a bit of manipulation in the slots to get a good connection to start charging. I did not experience any chronic issues with early NiMH termination or battery type identification that occurred with the VC4SL charger.
The XTAR VX4 is a basic analyzing charger, and can test the capacity / grading of all compatible battery types. It is also the first and only charger that can grade 1.5V Li-ion batteries. This capacity testing is only performed on discharge. The grading cycle will charge, discharge, and then charge again. During grading, charging is at 0.5A, and discharge is 0.3A, thus higher capacity batteries such as 21700s may take around a day to test. There are other more advanced chargers such as the Vapcell S4+ and V3.0 that can test both discharge and charge, however for most consumers, discharge testing should be adequate.
Some capacity testing results:
XTAR 1620mWh 1.5V Li-ion AAA - 973mAh / 1376mWh.
XTAR 4150mWh 1.5V Li-ion AA - 2525, 2593mAh / 3548, 3699mWh.
Panasonic 3500mAh NCR 18650GA (8 years old!) - 3224, 3334, 3294, 3151mAh.
IKEA LADDA 750mAh NiMH AAA (Grey) - 733mAh.
IKEA LADDA 2450mAh NiMH AA (Grey) - 2486mAh.
The results were roughly what I would be expecting. It should be noted that capacity testing results will vary between different models of analyzing chargers due to inconsistencies in max and minimum voltage, termination method, and discharge current. Capacity testing may not always work with protected Li-ion batteries if the batteries' protection circuit stops the charge or discharge before the charger.
The VX4 is passively cooled with no fans. There are some ventilation slots on the underside, along with some small (and not particularly grippy) feet.
User Interface
The XTAR VX4 has a large display, and 3 buttons. Batteries are inserted the "usual way" with +ve pole at the top of the charger, towards the display.
The XTAR VX4 has a blue LCD display with an automatic energy saving function. Depending on the functionality in progress, the VX4 can display mode, battery type, real time voltage (to 2 decimal places), real time charging current, real time capacity charged, capacity tested, battery "full" (charging terminated) status, grading cycle "done" status, and reverse polarity detected "err". There are no audible alerts to inform the user that charging is complete. Some people may like this, some might not. There is no display of battery temperature, internal resistance, or percentage charged. The latter may be a design decision as this reading isn't possible with 1.5V Li-ion batteries. There appears to be no temperature sensing.
There are 3 buttons, C/V, Mode, and mWh/mAh.
C/V button:
Single click - changes charging current levels (high to low steps, the charger may automatically limit the maximum allowed current).
Long press - switches between normal (3.6/3.7V Li-ion) and (3.2V) LiFePO4 modes.
Mode button:
Single click (during charging) - switches display between real time charging current and charged capacity.
Long press (during charging) - switches between charging and capacity testing modes.
mWh/mAh:
Single click (during 1.5V Li-ion) - switches between mWh and mAh display during 1.5V capacity testing.
Long press - turns off backlight.
I quite like the user interface. It is easy to use and I rarely had to consult the manual after the first read, which is great for a consumer orientated charger.
Conclusion
Positives:
Excellent range of battery size compatibility.
Excellent range of battery type compatibility including 1.5V Li-ion.
Can charge different battery types at the same time.
Real time charging display with voltage to 2 decimal places.
Analyzing (capacity testing/grading) functionality of all compatible battery types.
Reasonably priced.
Simple to use.
Easy to insert and remove batteries.
Negatives:
No battery temperature sensing or display.
No battery internal resistance display.
No battery percentage charged display.
Cannot select different charging currents for each slot.
Only tests capacity on discharge.
Limited to 1A charging when 4 bays are in use.
NiMH charging limited to 0.5A.
No audible alerts for charging complete.
The XTAR VX4 has an excellent range of battery compatibility, includes basic analyzing functionality, and is very easy to use. It is XTAR's most compelling new charger for some time. If you don't need 1.5V Li-ion compatibility or you need more advanced/enthusiast level analyzing functionality (such as internal resistance measurement) then I would consider alternative analyzing charger options. If you require 1.5V Li-ion compatibility, or just want an easy to use consumer orientated analyzing charger, then the XTAR VX4 is highly recommended.
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I bought the VX4 about a month ago to grade all of my 18650 cells. Cells with a higher internal resistance (I did the manual discharge method so my values are probably just relative to one another) fail in it, either constantly cycling charge/discharge/charge/etc… or switch to charge mode. I returned it and the new one did exactly the same thing.
Am I missing something or do you think this is a flaw?