Efest Slim K4 Battery Charger

Efest Slim K4 Battery Charger – Compact, Intelligent Charging for Multiple Cell Sizes

The Efest Slim K4 is a portable, four-bay lithium-ion battery charger designed for vapers and electronics enthusiasts who need a reliable, efficient, and travel-friendly solution for charging multiple battery formats. Supporting a wide range of battery sizes and powered by a Type-C USB input, the Slim K4 is built for convenience without compromising on performance.

Wide Battery Compatibility

The Slim K4 supports the most commonly used battery sizes in the vaping and flashlight industries, including high-drain lithium-ion cells. Compatible sizes include:

10440, 14500, 16340, 17340, 18350, 18490, 18500, 18650, 20700, 21700, 26500, and 26650.

This makes the K4 an ideal choice for users with a variety of devices, eliminating the need for multiple chargers.

Note: Batteries are not included with the charger.

Efficient Multi-Bay Charging with Intelligent Current Distribution

The Slim K4 automatically adjusts charging currents based on the number of batteries inserted:

• 1 or 2 batteries: Charges at up to 1A or 2A (per slot)

• 3 or 4 batteries: Charges at 0.5A per slot to ensure safe, balanced charging

Constant current (CC) charging currents are carefully regulated:

• 2 x 1A CC Current: 2000mA ±10%

• 1 x 1A CC Current: 1000mA ±10%

• 4 x 0.5A or 3 x 0.5A CC Current: <100mA per slot to avoid overloading the power input

Smart Charging Logic

The Slim K4’s smart circuitry monitors each slot independently. Batteries with different charge levels and chemistries can be inserted simultaneously without affecting charge safety or efficiency.

Additional technical protections include:

• Auto Recharge Activation: Triggers when voltage drops to 4.10V ±0.10V

• Auto Cut-Off Voltage: Stops charging at 4.20V ±0.05V

• Activation Current: Safely wakes depleted batteries (50mA – 100mA)

Compact, Travel-Friendly Design

Constructed with a slim, durable chassis and piano-wire spring contacts, the Slim K4 is built for long-term reliability. Despite supporting four cells, it remains lightweight and portable, ideal for users who travel frequently.

The integrated battery life LED indicators on each slot clearly display charging progress at a glance.

USB Type-C Input for Modern Convenience

The Slim K4 is powered via USB Type-C, providing efficient, reversible connectivity and allowing users to charge from wall adapters, power banks, laptops, or car chargers. This flexibility makes it especially convenient for on-the-go charging without proprietary cables.

Input Power: DC 5V / 2A recommended for optimal performance.

Technical Specifications

Package Contents

• 1 x Efest Slim K4 Charger

• 1 x USB Type-C Cable

• 1 x User Manual

Recommended Usage

The Efest Slim K4 is best suited for:

• Vapers charging 18650, 20700, or 21700 batteries for mods

• Flashlight enthusiasts using various lithium-ion cell sizes

• Users who need multiple battery charging in a slim form factor

• Anyone looking for a travel-friendly charger that works with a standard USB-C cable

Practical Performance

With its intelligent charging management, broad compatibility, and durable design, the Slim K4 is a practical solution for anyone managing multiple battery-powered devices. The Type-C input adds modern convenience, and the compact footprint makes it easy to pack for travel or daily carry.

Final Thoughts

The Efest Slim K4 combines portability with smart charging safety, making it a well-rounded choice for vapers and hobbyists alike. Its ability to efficiently handle multiple battery formats in a slim, USB-powered form makes it one of the more versatile chargers in its class.