The Xtar VX4 is a universal charger and capacity tester that breaks the boundaries of compatibility. It is designed for 3.7V/3.6V Li-Ion, NiMH/NiCd and newly supports 1.5V Li-ion and 3.2V LiFePO4 batteries. Thanks to the extended slots (supporting lengths of 34–80 mm), it accommodates even the longest protected 21700 batteries with protection electronics.

The charger features two selectable modes for different chemistries: Standard (for 3.6V/3.7V Li-ion, 1.5V Li-ion, and NiMH) and LiFePO4 mode (for 3.2V LiFePO4). Each slot is controlled independently, allowing you to charge different types of batteries simultaneously (mixing is possible within the selected mode). The clear LCD display shows voltage, capacity, and current. A useful feature is the capacity measurement (Grading) capability for all supported batteries, including modern 1.5V Li-ion batteries. Warning: USB versions of 1.5V Li-ion batteries may have limited compatibility. In Grading mode, the charger often runs them in an infinite cycle.

The maximum charging current is up to 3000 mA (1 slot) when using a USB power source with an output of at least 20W. For 3.6V/3.7V Li-ion and LiFePO4, the current can be manually regulated. If a battery has high internal resistance, the charger automatically reduces the current regardless of the manual setting to prevent the battery from overheating. For 1.5V Li-ion and NiMH batteries, the current is fixed at a safe 500 mA.

Parameters of the Xtar VX4 USB charger

• Four independently monitored charging channels.
• Physical compatibility: Supports batteries with a length of 34 to 80 mm (ideal for long protected 21700s) and a diameter of 10 to 32 mm.
• Protocol support: Recommended PD2.0 (12V 1.67A) for maximum performance. Also supports QC3.0 (9V 2A) and 5V 2A (with limited performance).
• Supported battery sizes:
  • 3.6/3.7V Li-ion & 3.2V LiFePO4: 32650, 26650, 25500, 22650, 21700 (including protected), 20700, 18700, 18650, 18500, 18490, 18350, 17670, 17500, 17335, 16340/RCR123A, 14650, 14500, 10440.
  • 1.5V Li-ion: AA, AAA.
  • NiMH/NiCd: D, C, SC, AA, AAA.
• Charging current:
  • 3.6V/3.7V Li-ion / LiFePO4: Manually selectable 0.25 A, 0.5 A, 1 A, 2 A, 3 A. (Max: 1x 3 A, 2x 2 A, 4x 1 A).
  • 1.5V Li-ion / NiMH: Fixed current 0.5 A (safe charging for small cells).
• Discharging current: fixed 0.3 A for all types of batteries. 
• If a battery has high internal resistance, the charger automatically reduces the current regardless of the manual setting to prevent the battery from overheating.
• Grading function (Capacity test): The charger can measure the real battery capacity via a charge-discharge-charge cycle. The measured energy can be displayed in mAh or mWh. This is the only way to determine the capacity of 1.5V Li-ion batteries.
• The LCD display shows the charging status, current, and capacity. The display can be turned off for undisturbed sleep (long press the C/V button).
• Charger weight: 315 grams. Dimensions: 172 x 130 x 41.5 millimeters.
• Advanced features: 0V activation (revival of over-discharged batteries), Soft Start, defective battery detection.
• The package includes the charger and a USB-C cable (power adapter is not included, we recommend a 30W USB adapter or a 45W USB car adapter).

Operation and Charging

Connect the charger to a USB power source. The default is Standard mode (suitable for 3.7V Li-ion, 1.5V Li-ion, and NiMH). If you want to charge LiFePO4 (3.2V), you must switch to LiFePO4 mode by long pressing the "Mode" button (the text LiFePO4 will light up on the display). Attention: You must not charge regular 3.7V Li-ion batteries in this mode (they would not be fully charged).

Button functions:

• C/V (Current/Voltage): A short press changes the charging current (only for 3.7V Li-ion and LiFePO4). A long press turns the display backlight on/off.
• Mode: A short press switches the displayed values (Current / Capacity / Internal resistance). A long press is used to change the chemistry (Standard vs. LiFePO4) or to select the Grading (capacity test) function, depending on the charger's status.
• mAh/mWh: Switches the displayed energy units (useful for comparing 1.5V batteries).

Warning

• When charging 1.5V Li-ion batteries, voltage and increasing capacity are not displayed in real time (only the final result is shown). To determine the capacity, use the Grading mode.
• Do not charge LiFePO4 in standard mode (risk of overcharging and battery damage).
• Do not charge primary (disposable) cells.
• The charger features reverse polarity and short circuit protection (it will display "ERR").