Fall Clearance
Efest Slim K4 USB C Charger
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Original price was: $24.99.$10.99Current price is: $10.99.
Fall Clearance price, already marked down. Codes don’t apply. While supplies last.
The Efest Slim K4 USB C Charger is a four-bay USB-C charger for 3.6V and 3.7V Li-ion and IMR batteries, including 21700s. It charges at 1A each for one or two batteries, or 0.5A each for three or four.
In stock
Most orders ship within 24 hours, except holidays and weekends. Orders placed on a weekend or holiday start processing the next business day.
| Option | Under $99 | $99 or more* |
|---|---|---|
| Standard shipping3–7 business days once shipped | $8.00 | FREE |
| PUDOpoint pickup3–5 business days, at a local counter | $8.00 | FREE |
| Adult signature (21+)Every shipped order | $8.00 | $8.00 |
Federal law requires an adult signature on every vape delivery: someone 21 or older signs and shows a valid photo ID.
Efest Slim K4 USB C Charger Review
The Efest Slim K4 USB C Charger is a four-bay USB-C charger for 3.6V and 3.7V Li-ion and IMR batteries, including 18650s and 21700s. It charges one or two batteries at 1A each, or three or four at 0.5A each, from a 5V 2A USB adapter. See more from Efest or browse all battery chargers.
Slim K4 Highlights
Automatic Current
It sets the current by how many batteries are in: 1A each for one or two, and 0.5A each for three or four.
USB-C Input
It runs from a 5V 2A USB adapter through its USB-C port, and the cable comes in the box.
LED Indicators
Each bay’s LED indicator shows white while the battery charges and turns blue when it’s full.
Built-In Protection
Efest lists short-circuit and reverse polarity protection, automatic over-charge and over-discharge protection and 0V activation recovery.
Slim K4 Specs
Charging
- Bays: 4
- Batteries: 3.6V and 3.7V Li-ion and IMR
- Charge voltage: 4.2V
- Charge current: 1A each for one or two batteries, 0.5A each for three or four
- Charging mode: CC and CV
Battery Sizes
- Li-ion, IMR: 12 sizes from 10440 to 26650, such as 14500, 16340, 18350, 18650, 20700, 21700 and 26650
K4 Charger
- Input: USB-C, 5V 2A
- Display: one LED indicator per bay: white while charging, blue when full
- Protection: short circuit, reverse polarity, over-charge and over-discharge, with 0V activation recovery
- Size: 117 × 107 × 29mm
- Body: fire-retardant ABS
Slim K4 Charge Current
Efest gives these currents:
| Batteries charging | Current per battery |
|---|---|
| 1 | 1A |
| 2 | 1A each |
| 3 | 0.5A each |
| 4 | 0.5A each |
Batteries
Charge only rechargeable 3.6V or 3.7V Li-ion and IMR batteries, never NiMH, alkaline or other single-use cells, and don’t leave the charger unattended while it’s plugged in.
How to Use the Slim K4
- Plug it in: connect the USB-C cable from the box to the charger and a 5V 2A USB adapter.
- Load the batteries: insert each battery with its ends matching the + and − marks. Efest says charging starts on its own within a few seconds.
- Watch the lights: each bay’s light shows white while it charges and turns blue when the battery is full.
Who the Slim K4 Is For
It suits vapers who charge up to four 18650 or 21700 batteries from a USB adapter. For two bays, see the Slim K2, or for a screen and 2A charging, the LUC V4 Elite.
Good to know: No wall adapter comes in the box. Efest rates the input at 5V 2A, so use an adapter that supplies 2A.
What’s in the Slim K4 Box
- Efest Slim K4 charger
- USB-C charging cable
- User manual and warranty card
Efest Slim K4 FAQ
Does it charge 21700 batteries?
Yes. Efest lists 21700 and 20700 batteries, along with 18650s and 26650s. We sell IMREN 21700 batteries in 2-packs.
How fast does it charge?
1A per battery with one or two in, and 0.5A per battery with three or four in.
Does it come with a wall adapter?
No. It comes with a USB-C cable. Use a USB adapter rated for 5V 2A.
What do the lights mean?
White means the battery is charging. Blue means it’s full, or the bay is on standby.
Can it charge AA or NiMH batteries?
No. Efest lists 3.6V and 3.7V lithium batteries only.
How is it different from the Slim K2?
The Slim K2 has two bays and charges both batteries at 1A each. The K4 has four bays and drops to 0.5A each with three or four batteries in.
Compatible With...
18650 · 2600mAh · 60A
21700 · 3750mAh · 40A
20700 · 3200mAh · 40A
18650 · 3500mAh · 20A
20700 · 3400mAh · 40A
18650 · 2500mAh · 35A
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