The Nitecore UM4 is an intelligent, four-slot USB battery charger that supports Quick Charge (QC) 2.0 and can charge a wide array of rechargeable battery types. Each slot is independently controlled, allowing you to charge different batteries simultaneously.
Specifications
Input: DC 5V/2A or 9V/2A, 18W (Max).
Output Voltage: 4.35V ±1% / 4.2V ±1% / 3.7V ±1% / 1.48V ±1%.

Output Current:
QC Mode: 1,500mA x 1, 1,500mA x 2, or 750mA x 4.
Standard Mode: 1,500mA x 1, 1,000mA x 2, or 500mA x 4.
Compatible Batteries: The UM4 supports various IMR, Li-ion, LiFePO4, Ni-MH, and Ni-Cd battery sizes, including common types like 18650, 21700, AA, and AAA.
Dimensions: 159mm x 107mm x 41mm.
Weight: 232.8g.

Key features
Intelligent charging: The charger automatically detects battery type and capacity to apply the optimal charging strategy.
Real-time LCD display: An informative display shows details like voltage, current, and charging progress.
Manual control: Users have the option to manually adjust charging current and cut-off voltage for certain batteries.
Independent slots: Each of the four slots operates independently.
Quick Charge 2.0: Supports faster charging speeds with compatible power sources.
Safety features: Includes various protections such as reverse polarity and short circuit prevention, along with features for activating over-discharged batteries and restoring IMR batteries.
Durable construction: Built with fire-retardant materials and designed for efficient heat dissipation.

The Nitecore UM4 is a four-slot intelligent charger that offers multiple safety features and customization options for various battery types. To use it safely, you must select the correct settings for your specific batteries, especially LiFePO4 and 3.8V Li-ion cells, as improper charging can lead to fire or explosion.

General safety precautions

Use only rechargeable batteries: Never attempt to charge non-rechargeable cells, such as alkaline, CR123A, or CR2 batteries.
Inspect batteries before charging: Do not charge any battery that shows damage, such as swelling, dents, or tears in the outer wrapper.
Check the power source: Use only the official Nitecore cable and a compatible USB adapter (QC 2.0 is recommended for maximum speeds). Unofficial or damaged cables can cause overheating and other issues.
Charge in a safe location: Always charge batteries on a non-flammable, fireproof surface. Do not leave the charger unattended and unplug it when not in use.
Keep away from heat and moisture: Operate the charger in a well-ventilated area away from direct sunlight, open flames, and high humidity.
Avoid misuse: Do not short-circuit the batteries or the charger. Never disassemble or modify the device.

Safety features of the UM4
Overtime charging protection: The charger automatically stops charging any slot that exceeds 20 hours to prevent overheating from faulty batteries.
Reverse polarity and short-circuit protection: If you insert a battery incorrectly or if there’s a short circuit, the LCD screen will display “EE EE,” and the charger will not operate.
Over-discharged battery restoration: The UM4 can attempt to restore depleted IMR and Li-ion batteries. For over-discharged IMR batteries, the reverse polarity protection is temporarily disabled during restoration, so you must ensure correct polarity.
Temperature regulation: A built-in system protects the charger from overheating during the charging process.
Automatic internal resistance detection: The charger displays a battery’s health as “Good” or “Poor,” indicating when a cell may need to be replaced.

Operating instructions
After connecting the charger to a power source and inserting batteries with correct polarity, the UM4 automatically detects and begins charging standard 3.7V Li-ion and Ni-MH/Ni-Cd batteries. For LiFePO4 and 3.8V Li-ion batteries, manual adjustment of voltage is needed using the C and V buttons. You can also adjust the charging current in 100mA increments. The LCD screen shows real-time information. Charging stops automatically when complete.

charger

Nitecore UM4 Charger