The 10 best 3.7v battery charger 4.2v

Finding the best 3.7v battery charger 4.2v suitable for your needs isnt easy. With hundreds of choices can distract you. Knowing whats bad and whats good can be something of a minefield. In this article, weve done the hard work for you.

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Samsung High Drain INR18650-25R 20A 2500mAh Rechargeable Flat Top 3.7V Battery, (2 Pcs) by M&A BD Electronics Samsung High Drain INR18650-25R 20A 2500mAh Rechargeable Flat Top 3.7V Battery, (2 Pcs) by M&A BD Electronics
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Nitecore New i4 2016 Intellicharger Smart Battery Charger for Li-ion IMR Ni-MH NiCd Nitecore New i4 2016 Intellicharger Smart Battery Charger for Li-ion IMR Ni-MH NiCd
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WishDeal 4 x 2000 mAh 3.7V Rechargeable Battery with Smart Charger Button Top Rechargeable Battery for Flashlight LED Torch WishDeal 4 x 2000 mAh 3.7V Rechargeable Battery with Smart Charger Button Top Rechargeable Battery for Flashlight LED Torch
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Arlo Certified: Tenergy 3.7V Arlo Battery Fast Charger and 650mAh RCR123A Li-ion Rechargeable Batteries for Arlo Wireless Security Cameras (VMC3030/3200/3330/3430/3530), UL UN Certified, 4-Pack Arlo Certified: Tenergy 3.7V Arlo Battery Fast Charger and 650mAh RCR123A Li-ion Rechargeable Batteries for Arlo Wireless Security Cameras (VMC3030/3200/3330/3430/3530), UL UN Certified, 4-Pack
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Smiling Shark 18650 Lithium Rechargeable Batteries 4200mAh 3.7V (2 Pack) and Smart Universal Rechargeable Battery Charger for Li-ion 10440 14500 1340 16650 18500 18650 2665 with USB Charging Cable Smiling Shark 18650 Lithium Rechargeable Batteries 4200mAh 3.7V (2 Pack) and Smart Universal Rechargeable Battery Charger for Li-ion 10440 14500 1340 16650 18500 18650 2665 with USB Charging Cable
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Universal Intelligent Smart Battery Charger for 3.7V Li-ion Packs (4.2V 1000mA Output) Universal Intelligent Smart Battery Charger for 3.7V Li-ion Packs (4.2V 1000mA Output)
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IMREN Green Series IMR 18650 High Drain 3200mAh Li-ion 20A / 40A 3.7V Rechargeable Flat Top Battery, (4 Pack With Hard PC Protection Case) by M&A BD Electronics IMREN Green Series IMR 18650 High Drain 3200mAh Li-ion 20A / 40A 3.7V Rechargeable Flat Top Battery, (4 Pack With Hard PC Protection Case) by M&A BD Electronics
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4.2V 1A Power Adapter Li-ion Battery Charger With LED indicator 5.5x2.5 / 2.1mm Interface Suitable for 3.7V 4.2V 1-string Lithium Battery Pack 4.2V 1A Power Adapter Li-ion Battery Charger With LED indicator 5.5x2.5 / 2.1mm Interface Suitable for 3.7V 4.2V 1-string Lithium Battery Pack
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CIVICTOR 26650 18650 Charger 4.2V Protected USB Power Bank External Battery DIY Case Holder Portable Fast Single 3.7V 3.6v 3.7 Volt Lithium ion Li-ion Rechargeable 18650 Battery Charger Flashlight CIVICTOR 26650 18650 Charger 4.2V Protected USB Power Bank External Battery DIY Case Holder Portable Fast Single 3.7V 3.6v 3.7 Volt Lithium ion Li-ion Rechargeable 18650 Battery Charger Flashlight
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2-Bay Smart Li-ion Battery Charger, for 18650, 26650, 18500, 17335, 3.7V AA, AAA Rechargeable Lithium Batteries, Flashlight Torch headlamp Charger, USB Port Dual Channel with LCD 2-Bay Smart Li-ion Battery Charger, for 18650, 26650, 18500, 17335, 3.7V AA, AAA Rechargeable Lithium Batteries, Flashlight Torch headlamp Charger, USB Port Dual Channel with LCD
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Reviews

1. Samsung High Drain INR18650-25R 20A 2500mAh Rechargeable Flat Top 3.7V Battery, (2 Pcs) by M&A BD Electronics

Feature

CHARACTERISTICS - Ideal for Device That Requires Removable Flat Top 18650 Size Battery, Chemistry: INR, Model: 25R, Size: 18650, Style: Flat Top, & Type: Lithium-ion
SPECIFICATIONS - Capacity: 2500mAh (MAX), Continuous Rated Discharge: 20A (MAX), & Nominal Voltage: 3.6V-3.7V
GENERAL KNOWLEDGE TIPS - Fully Charged to 4.2V Before First Use & Use Only Proper Battery Charger That's Designed for 18650 Type Battery
BATTERY LIFE CYCLE & STORAGE TIPS - Capacity Drops to 60% After 250 Full Charge/Discharge Cycles & Must Store the Battery in a Proper Case/Box in a Cool & Dry Place
OUR GUARANTEE (Only Offer by Seller "M&A BD Electronics") - 100% Satisfaction, 100% Brand New Batteries, & Each Quantity Order Comes With 2 Batteries in Double Packed Boxes

Description

Specs:
  • Style: Flat Top
  • Chemistry: INR
  • Nominal capacity: 2500 mAh (Max)
  • Max Continuous Rated Discharge: 20A (at -20 to 75 degrees Celsius)
  • Dimensions: 64.85 0.15 mm (L) x 18.33 0.07 mm (D)
  • Weight: 45g (Max)
  • Discharge Cut-off Voltage: 2.5V
  • Nominal voltage: 3.6~3.7V
  • Full Charge Voltage: 4.2V 0.05V
  • Protected: No, Unprotected
  • Cycle info: Capacity drops to 60% after 250 full charge/discharge Cycles
  • Standard Charge: Constant Current 1250mA, Constant Voltage 4.2V, & Cut-Off 100mA
  • Rapid Charge: Constant Current 4000mA, Constant Voltage 4.2V, & Cut-Off 100mA
  • Operational Charging Temperature Range: 0 to 50 degrees Celsius (best below 45 degrees Celsius)
  • Operational Discharging Temperature Range: -20 to 75 degrees Celsius (best below 60 degrees Celsius)
What You Will Receive:
  • Samsung INR18650 25R Flat Top Rechargeable Battery x2

2. Nitecore New i4 2016 Intellicharger Smart Battery Charger for Li-ion IMR Ni-MH NiCd

Feature

Twice the charging speed of the i4 charger, up to 1.5A. Compatible with 1.2V, 3.7V, 4.2V, 4.35V batteries
Optimized charging design for IMR batteries, with new IMR battery recovery feature
Automatically detects battery power status and displays charging progress, and automatically stops charging when complete
For use with Li-ion / IMR / LiFePO4: 10340, 10350, 10440, 10500, 12340, 12500, 12650, 13450, 13500, 13650, 14350, 14430, 14500, 14650, 16500, 16340(RCR123), 16650, 17350, 17500, 17650, 17670, 18350, 18490, 18500,18650, 18700, 20700, 21700, 22500, 22650, 25500, 26500, 26650; Ni-MH / NiCd: AA, AAA, AAAA, C, D
For use with Rechargeable batteries only. Do not attempt to charge primary cells such as Alkaline, Zinc-Carbon, Lithium, CR123A, CR2 or any other unsupported chemistry

Description

Features
  • Active Current Distribution (ACD) Technology
  • Compatible with 1.2V, 3.7V, 4.2V, 4.35V batteries
  • Capable of charging four batteries simultaneously
  • Automatically detects battery power status and displays charging progress
  • Made from fire resistant, flame retardant PC material
Specifications:
Input Voltage: AC 100~240V 50/60Hz 0.25A (max) 10W DC 9~12V 1A
Output voltage: 4.35V1% / 4.2V1% / 3.7V1% / 1.48V1%
Output current: 1.5A x 1 / 0.75A x 2 / 0.5A x 2 / 0.375A x 4

Compatible with:
--Li-ion / IMR / LiFePO4: 10340, 10350, 10440, 10500, 12340, 12500, 12650, 13450, 13500, 13650, 14350, 14430, 14500, 14650, 16500, 16340(RCR123), 16650, 17350, 17500, 17650, 17670, 18350, 18490, 18500,18650, 18700, 20700, 21700, 22500, 22650, 25500, 26500, 26650 --Ni-MH / NiCd: AA, AAA, AAAA, C, D

Weight: 202g

Safety Precautions:
  • For use with Li-ion, IMR, LiFePO4, Ni-MH/Ni-Cd rechargeable batteries only
  • Do not leave working charger unattended
  • Do not attempt to charge primary cells such as Alkaline, Zinc-Carbon, Lithium, CR123A, CR2 or any other unsupported chemistry
  • Never charge / discharge battery having evidence of leakage, swelling, damaged outer wrapper, color-change or distortion
  • Do not touch hot surfaces. Batteries or device may become hot at full load or high power charging/discharging
  • Remove all batteries and unplug charging unit from power source when not in use
  • See Included User Manual for additional Safety Instructions
Warranty Locate verification code on package box and register at http://charger.nitecore.com/validation. You will receive a warranty service email response. If any problems are encountered during registration, contact manufacturer directly at http://www.nitecore.com/contactus/

3. WishDeal 4 x 2000 mAh 3.7V Rechargeable Battery with Smart Charger Button Top Rechargeable Battery for Flashlight LED Torch

Feature

Matterial: Rechargeable Li-ion Battery; Volt: 3.7 V
Battery Type: Button Top battery, Not AA OR AAA Battery, Rechargeable
Battery Capacity: 2000 mAh. It will last 4 - 5 hours if you use the battery on 1200 Lumnes Flashlight. It will last 2 hours if you use the battery on 8000 Lumens.
Note: It is BUTTON TOP. ( NOT FLAT TOP) NOT FOR The Devcies Which Match Flat Top Battery Like Vape,Ship From US.
It will arrive to you around 3 to 5 working days.If you have any question, pls contact us without Hesitation. We will try our best to service you.

Description

Specifications:
Battery Size:Height: 65 mm*Diameter: 18 mm
Battery type: rechargeable battery
Voltage:3.7V(2.5V-4.2V)
Capacity:2000mAh
Net Weight:45g/1pcs
Diameter: 0.72 in
Length: 2.6 in



Smart Battery Charger:
It is with high efficiency and reliability! High Quality 2 Slots Charger for 18650 Battery.
Quick charge with automatic constant current control prevents battery from overcharging, short circuit, and electronic shock.
Input Voltage: AC 100V - 240V 50 / 60Hz Max150mA
Output Voltage: DC 4.2V 650mA
Battery Type: 4 x rechargeable battery
Rechargeable Time Limit: About 2 hours
Dimensions: 1.73" x 1.26" x 3.27" (L x W x H)



WARNING:
DO NOT dispose in fire or heat;
DO NOT puncture,damage,and disassemble;
DO NOT mix fresh batteries with used batteries



Package:4 x 3.7V Rechargeable Battery
1 x Dual Cahrger

4. Arlo Certified: Tenergy 3.7V Arlo Battery Fast Charger and 650mAh RCR123A Li-ion Rechargeable Batteries for Arlo Wireless Security Cameras (VMC3030/3200/3330/3430/3530), UL UN Certified, 4-Pack

Feature

BATTERY FOR ARLO SECURITY CAMERAS - The world's only innovative rechargeable RCR123A Lithium Ion Battery specifically designed to work with Arlo Security Cameras seamlessly. Works with Arlo Wire-Free HD Security Cameras (VMC3030/3200/3230/3330/3430/3530) **Only use Tenergy Arlo Battery Charger (Part Number 01451) to charge these batteries. Using other brands or models may result in incomplete charge of batteries.**
REUSE & SAVE - The Tenergy Arlo Camera Battery can be recharged up to 500 times. The reusability offers significant savings over non-rechargeable batteries. Very convenient usage and a drop-in replacement. Also saves our environment by preventing the waste of non-rechargeable Lithium CR123A batteries. **Charger is intended for use only with the Tenergy RCR123A Lithium Ion Battery, charging other types of batteries could cause explosion or fire**
SMART PROTECTION - Built-in protection circuit actively manages battery performance during charging and discharging. Helps detect and prevent over-charge, over-discharge, short-circuit, or over-current by shutting off the device or charger. **Protection features does not offer safeguards when batteries other than the Tenergy RCR123A Lithium Ion Battery is used.**
CERTIFIED FOR SAFETY - Extensively tested and certified by the most stringent battery safety standard: UL 1642, UL 2054, UN 38.3, IEC 62133, UL 60950, Battery Directive (2006/66/EC), CSTCG (PI965).
BOX CONTENTS - Package comes with 4 x Tenergy 3.7V Arlo Security Camera Battery

Description

Charger and Battery For Arlo Security Camera
Lithium-ion rechargeable batteries and specifically designed to work with Arlo Security Cameras seamlessly. Works with Arlo Wire-Free HD Security Cameras (VMC3030)

Advanced, Sophisticated Charging Safety
Built-in protection against reverse-polarity and short-circuit for total charging safety. Built-in temperature sensor catches and prevents charging induced over-heating. Charger body made of fire retardant materials. Also features safety timer which will automatically shut off the charger in 3 hours to prevent over-charge and to give you peace of mind charging Li-ion RCR123A batteries.

Certified for Safety and Power Efficiency
Battery: Extensively tested and certified by the most stringent battery safety standard: UL 1642, UL 2054, UN 38.3, IEC 62133, UL 60950, Battery Directive (2006/66/EC), CSTCG (PI965).

Charger: Certified for international CE and FCC safety standards. It has also been certified to Californias CEC standard to ensure power efficiency. Charger Adapter with UL certification.

Other Technical Specifications:
Charger:
Compatible with Tenergy 3.7V 650mAh RCR123A Li-ion Rechargeable Battery only. Do not charge any other type of battery.
Input: 100-240V AC 50/60Hz
Output: 4.2V DC, 400mA x 4 (1600mA Max)
Dimensions: 3.6 x 3.1 x 1 inch

Battery:
Battery Size: RCR123A (16340)
Battery Type: Li-ion Rechargeable
Voltage: 3.7V
Capacity: 650mAh
Charge up to 500 times
Dimensions: 16.9mm (diameter) x 34.3mm (length)
UL and UN Certified

Package Contents:
4 x RCR123A Li-Ion 650mah Rechargeable Batteries
1 x Tenergy RCR123A Li-ion Rechargeable Battery Charger
1 x Power Adapter

5. Smiling Shark 18650 Lithium Rechargeable Batteries 4200mAh 3.7V (2 Pack) and Smart Universal Rechargeable Battery Charger for Li-ion 10440 14500 1340 16650 18500 18650 2665 with USB Charging Cable

Feature

Universal Charger---Suitable for 3.7V li-ion battery 26650 18650 18500 18350 16650 1634014500 10440. 2 x 4200mAh 18650 Rechargeable Batteries are Included.
Powerful Battery: High power capacity of 4200 mAh, longer run time than all of cheap batteries labeled 2250mAh or 3000mAh.
Fast Charger---use smart chip technology, higher electric output current and quicker charging, 4 hours can charged 95% power, better than these cheap chargers.
Durable and High Quality: High energy density, long life battery This battery has an extra long life for all your battery powered devices
100% money back & satisfaction guarantee - If you are not completely satisfied with our battery charger we offer 30 days money back.

Description

3.7V 18650 Rechargeable Battery:
Size: 18mm x 65mm
No memory effect
Environmentally friendly
Battery Type: Rechargeable Battery
Capacity: 4200mAh
Material: Li-ion Battery
Color: Blue
Weight: 43grams
Standard voltage: 3.7V
Voltage of full charge: 4.2V
Voltage of cut-off discharge: 2.75V

WARNING:
DO NOT dispose in fire or heat;
DO NOT puncture,damage,and disassemble;
DO NOT mix fresh batteries with used batteries

Smart Battery Charger:
It is with high efficiency and reliability! Quick charge with automatic constant current control prevents battery from overcharging, short circuit, and electronic shock.
Input Voltage: DC 5V 1-2A
Output Voltage: DC 4.2V 1000mA
Suitable for 3.7V Li-ion Battery 26650 18650 18500 18350 16650 1634014500 10440
Conventional 5V power supply: computer, mobile phone charger, mobile power, car chager

Package Includes:
2 x 3.7 Rechargeable Battery
1 x Dual Smart Battery Charger

6. Universal Intelligent Smart Battery Charger for 3.7V Li-ion Packs (4.2V 1000mA Output)

Feature

Charges any 3.7V Li-ion Rechargeable Battery Packs. (Not for charging individual Li-ion unprotected cells)
Packs must have a built-in PCB (Protection Circuit Board)
Intelligent Smart Charger. Power cuts off when full.
Status light indicates charging status. Red if charging. Green when full.
Standard 5.25mm x 2.5mm power connector. 4.2V 1A Power Output. Standard US power plug

Description

This battery charger will charge any 3.7V 18650 Rechargeable battery packs. Comes with a 4ft Cable. Can be used with AC 110V and 240V. Uses standard US power socket . Battery packs must have a built-in PCB (Protection Circuit Board)

7. IMREN Green Series IMR 18650 High Drain 3200mAh Li-ion 20A / 40A 3.7V Rechargeable Flat Top Battery, (4 Pack With Hard PC Protection Case) by M&A BD Electronics

Feature

CHARACTERISTICS - Ideal for Electronic Device That Requires Removable High Drain 18650 Size Battery, Chemistry: IMR, Model: Green Series 3200mAh, Size: 18650, Style: Flat Top, & Type: Lithium-ion
SPECIFICATIONS - Capacity: 3200mAh (MAX), Continuous Rated Discharge: 20A (MAX), Rated 40A (MAX) Pulse, & Nominal Voltage: 3.6V-3.7V
GENERAL KNOWLEDGE TIPS - Fully Charged to 4.2V Before First Use & Use Only Proper Battery Charger That's Designed for 18650 Type Battery
BATTERY LIFE CYCLE & STORAGE TIPS - Capacity Drops to 60% After 250 Full Charge/Discharge Cycles & Must Store the Battery in a Proper Case/Box in a Cool & Dry Place
OUR GUARANTEE (Only Offer by Seller "M&A BD Electronics") - 100% Satisfaction, 100% Brand New Batteries, & Each Quantity Order Comes With 4 Batteries in Double Packed Boxes (Plastic Storage Case Included)

Description

Specs:
  • Style: Flat Top
  • Chemistry: IMR
  • Nominal capacity: 3200 mAh (Max)
  • Max Continuous Rated Discharge: 20A & Rated 40A Max Pulse
  • Dimensions: 65.00 0.20 mm (L) x 18.15 0.20 mm (D)
  • Weight: 47.4g (Max)
  • Discharge Cut-off Voltage: 2.5V
  • Nominal voltage: 3.6~3.7V
  • Full Charge Voltage: 4.2V 0.05V
  • Protected: No, Unprotected
  • Cycle info: Capacity drops to 60% after 250 full charge/discharge Cycles
  • Standard Charge: Constant Current 4000mA, Constant Voltage 4.2V, & Cut-Off 100mA
  • Operational Charging Temperature Range: 0 to 70 degrees Celsius (best below 70 degrees Celsius)
  • Operational Discharging Temperature Range: -20 to 70 degrees Celsius (best below 70 degrees Celsius)
What You Will Receive:
  • IMREN Green Series 3200mAh Flat Top Rechargeable Battery x4
  • Plastic Battery Storage Case x2 (For 4 Batteries)

8. 4.2V 1A Power Adapter Li-ion Battery Charger With LED indicator 5.5x2.5 / 2.1mm Interface Suitable for 3.7V 4.2V 1-string Lithium Battery Pack

Feature

Input voltage: AC 110V / 220V (AC90-264V suitable for anywhere in the world voltage level).

Output: DC 4.2V 1A (Suitable for 3.7V 4.2V 1-string Lithium Battery Pack)

Output Wire length: 1m / 3.28ft.

Output interface: 5.5 * 2.5mm / 2.1mm (With built-in leaf spring, Compatible with 5.5x2.5 / 2.1mm ).Before buying, be sure to confirm that the interface size of this product matches with yours. Wrong size will not work!!!

With over-current protection, over-discharge protection, over-voltage protection, overcharge protection, short circuit protection.Enter Protection mode , with flashing red light.

Description

NOTE:
1.Before buying, be sure to confirm that the interface size of this product matches with yours. Wrong size will not work!!! ( The interface size of this product is 5.5x2.5 / 2.1 mm).
2. This product has many kinds of protection functions, enter the protection mode, LED lights will flashing red light. When this happens, unplug the adapter immediately and check if the circuit is short-circuited, if the electrical power exceeds the rated power of the adapter, etc.

Parameter:
Input voltage: AC 110V / 220V (AC90-264V suitable for anywhere in the world voltage level).
Output: DC 4.2V 1A.
Output Wire length: 1m / 3.28ft.
Output interface: 5.5 * 2.5mm / 2.1mm
With built-in leaf spring, Compatible with 5.5x2.5 / 2.1mm.
With over-current protection, over-discharge protection, over-voltage protection, overcharge protection, short circuit protection.Enter Protection mode , with flashing red light.

Charging process LED indicator changes:
1. No-load status LED is green;
2. Charging, the first phase of constant current charging, LED indicator is red. Charge to the rated voltage into the second phase of constant voltage charging, the current slowly decreases.
3. When the battery power reaches 90-95%, LED lights turn green. At this point the charger will continue to charge with a small current until it is full.

Package Included:
1*4.2V 1A Power Adapter Li-ion Battery Charger

9. CIVICTOR 26650 18650 Charger 4.2V Protected USB Power Bank External Battery DIY Case Holder Portable Fast Single 3.7V 3.6v 3.7 Volt Lithium ion Li-ion Rechargeable 18650 Battery Charger Flashlight

Feature

Dual function: 26650 18650 Charger or portable Power bank for flashlight, headlamp if with 26650 battery or 18650 battery, 5V / 1A output; not suggest to charge big power device which required input more than 5V/1A
Protected 4.2V / 1A output smart charger for 3.7V lithium li-ion rechargeable batteries 18650 26650; so you never need worry about your love 18650 battery or 26650 battery be damaged in charging;
No power outlets to be supplied, Plugs into most any USB wall adapterCommenly USB port can be fitted for any 5V usb adptor by your usb cable or the supplied short usb cable, which only is a 3.93inch long cable be placed on the designed bottom of the smart charger, So you will never forget to take the charging cable on travel
4 pcs bright LED indicator helps you keep track of the current condition of power; A premium plastic cover lock your battery in, avoid your battery away collision
Deliveried: 1 * multi function usb charger / power bank; 1 * 10cm USB cable; 45 days money back guarantee, 24-Month Warranty; MCU Protection to avoid overcharged, overheat, wrong polarity charged

Description

Product Features:

Both Charge and Discharge Features: charging design for 18650/26650 batteries, as well as recharge mobile phones, flashlights, etc

Designed with a special slot to place the accessories 3.9 inch USB to mini USB cable to avoid the long harassment of your backpack

4 Led indicator lights to display the detailed charger status for ensure you better using the charger/power bank

Made from durable ABS, anti-drop 1M

Controlled by smart MCU can automatically turn to trickle charging, prevent the batteries from over-voltage, over-current or over-heat; Automatically stops charging when battery full; Features reverse polarity protection

Specifications

Input: DC 5V/1A with micro USB port, recharging battery is 4.2V/1A
USB discharging output: DC 5V/1A
Charging time for 3400mAh batteries is about 4 hours
Charging time for 2600mAh batteries is about 3 hours
Size: L107 mm x D34 mm x H 39 mm / 4.21 in x 1.34 in x 1.54 in
Weight : 65 g / 2.29 oz
Operating Temperature: -20 degrees C ~ 50 degrees C (full-load in normal working condition)
Operating Humidity: 5% (0 degrees C) ~ 90% (40 degrees C) 72 hours (Full-load in normal working condition)
Storage conditions: Temperature -20 degrees C ~ 85 degrees C

Packages

Battery charger with a protective cover x 1; manual x 1; USB to mini USB cable x 1

10. 2-Bay Smart Li-ion Battery Charger, for 18650, 26650, 18500, 17335, 3.7V AA, AAA Rechargeable Lithium Batteries, Flashlight Torch headlamp Charger, USB Port Dual Channel with LCD

Feature

The 18650 battery charger doesn't enclude batteries on the pic.
Support USB charging help travelers can charge lithium ion batteries anytime anywhere, especially when you don't have enough outlet,you can even simply plug into your laptop or other device.
Use to charge 3.7V Lithium rechargeable batteries only. Type and Size of Batteries Supported: 2-Bay Li-ion Battery charger can charge 26650, 18650, 18500, 18350, 17670, 17500, 16340, 14500, 10440 3.7V lithium battery and so on.Do not charge alkaline, carbon or any other type of battery not specified on the charger.
LCD screen of the 18650 usb charger can show the charging status. It tells you what volts it's charging at, what percentage it is currently at, it keeps the amount of time that it has been charging, and it has shows the % in single increments. It automatically stop charging if it's full or detecting improper usage.
Not afraid to leave batteries in the charger all the time: It automatically stop charging dual 18650 charger if it's full or detecting improper usage.

Description

2-Bay Intelligent Li-ion Battery Charger, USB Port Dual/Double-Channel Rechargeable Battery Charger with LCD for 18650, 18500, 26650, 14500 3.7V Smart Lithium Batteries

About the charger:

When your rechargeable batteries are out of power, you need a battery charger, and this 2-Bay Intelligent 3.7V Smart Lithium Batteries charger is a very good choice for you, and it could charge 2 pcs of 18650, 18500, 26650, 14500 Lithium battery. What's more, LCD screen of the 18650 charger can show the charging status. It tells you what volts it's charging at, what percentage it is currently at, it keeps the amount of time that it has been charging, and it has shows the % in single increments. It automatically stop charging if it's full or detecting improper usage.

Features

1. USB powered Li-ion battery charger.
2.High definition LCD of 2-Bay Smart Li-ion Battery Charger displays real time charging status, present voltage and capacity visually.
3. Features micro USB output charging.
4.Integrated intelligent power management system.
5.Intelligently detects input power.
6.Can selects charging current based on battery capacity
7.Features reverse polarity protection
8.Packed with color gift box.

Specifications

Input: Micro USB DC 5V, 1A/2A
Output: 4.2V, 1A / 0.5A
Compatible with: Li-ion: 26650, 18650, 18500, 18350, 17670, 17500, 16340, 14500, 10440 3.7V lithium battery and so on.
Dimensions: 5.1" x 2.6" x 1.4"
Weight:5.6 ounces

Conclusion

By our suggestions above, we hope that you can found the best 3.7v battery charger 4.2v for you. Please don't forget to share your experience by comment in this post. Thank you!