Efest IMR 21700 4000mAh 30A Rechargeable battery


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If you are a serious vaper you know the benefits of spare fully charged batteries, ready to go whenever or wherever you need them. E cigarettes generally take at least one (or two) 18650 or 21700 removable/rechargeable battery(ies). It is possible to charge these batteries internally within your vaporiser via USB but for the sake of battery longevity and more importantly for your personal safety, it is recommended that they be charged via an external charger (Yes, I also sell Efest chargers!). In this way you need never have any down time without any power.

21700 batteries are becoming a commonly used battery size for vaporisers. They produce the right amount of voltage and many of them can handle the high-current discharge necessary for vaping.

Let’s start with the basics – Efest batteries are all a very arresting shade of purple but unlike the 18650’s I sell these unfortunately do not come with an included case. These batteries are considered to be safe and powerful performance pieces, but you should treat them with great care and discard any that have punctures or are losing their wrapping.

Battery Specifications:

  • IMR 21700
  • 4000mAh
  • 30A
  • 7v
  • Flat top
  • Li-Mn
  • Length = 70 ± 0.2mm

Now some school time………..

Why the number 21700? These are not just random numbers, they mostly correspond to measurements of the battery. 21mm wide, 70mm long and 0 to denote that the battery is cylindrical.

What is mAh anyway? Stands for milliamp hour and is basically a unit that measures electric power over time and is commonly used to measure the energy capacity of a battery. In general, the more mAh the longer the battery capacity. A higher number means that the battery can store more energy resulting in less charging. Be cautious with batteries that have a very high mAh rating as they can be very dangerous (or they are lying to you about the capacity.)

30A? This is the continuous charge rate or amp limit. Basically, the maximum amount of current (amps) that you can continuously draw before it heats up to dangerous levels (usually above 75°C). Or more simply how fast the charge is flowing. To figure out how many amps you are pulling from your battery simple divide your power (wattage setting on your vape) by your battery voltage (most batteries have a voltage of 4.2v and nominal at 3.7v). If the answer is less than 20 you are good. Be aware though that the voltage of the battery decreases as it discharges effectively changing the equation.

3.7v? This refers to the batteries output range. Most vaping batteries have a charge voltage of 4.2 (peak performance rate), a nominal voltage of 3.7 (regular performance rate), and a voltage discharge cut off between 2 and 3 volts (a safety feature). Voltage can be easily explained as electrical potential between 2 places. It is the “push” that causes charges to move.

Flat top? 21700 batteries come in 2 varieties, flat top and button top. Button top batteries tend to be slightly longer so may not sit flush within your mod or result in a very tight fit. A benefit of button top is that it makes it easier to insert your batteries the right way up. Most modern vaporisers (spring loaded) easily accept flat top batteries. When using flat tops just make sure to check which side is positive and which side is negative. Efest batteries have markings showing you which side is positive and which is negative but if you are fumbling around in the dark the smoothest flattest end is negative (larger silver disc) and the other side is positive.

Li-Mn? Stands for lithium ion manganese oxide and are known to be very safe whilst still outputting a large amount of power. So safe that they are used primarily in medical devices (even within the body). They are also resistant to puncturing.

I could go on and on as the information around batteries is extensive. I recommend if you are unsure about your batteries do as much research as you can to ensure the highest level of safety possible.  Always make sure that you are choosing the correct battery for your device and usage levels.


  • Don’t touch conductive material (coins etc) to the positive end as this may short them and/or damage them.
  • If the battery wraps are torn or damaged in any way the negative contacts may become exposed. This is dangerous, and the batteries should be discarded safely.
  • Ensure that you are inserting the batteries the right way around.
  • Always purchase your batteries from trusted vendors.
  • Do not drop or mishandle batteries.
  • Do not unpeel the wrap or puncture in any way.
  • When transporting batteries put them in an appropriate container.
  • Do not leave your batteries in extreme temperatures such as hot car or a very cold location.
  • A good quality external charger will help maintain the integrity and life span of your batteries. A wise investment.
  • If using an external charger, it is important that the voltage of your charger matches the battery voltage. For 21700 batteries you should only use a charger that provides a voltage of 4.2 (Efest Lush chargers work a treat and are available!). Any higher and your battery may short and vent.
  • If your mod takes more than one battery make sure that they are “married”, essentially that they are charged together for the same length of time so neither have more power than the other.
  • A low charging current (usually between 0.5 and 2.0 amps) is also important as charging batteries too quickly will degrade them, decreasing the number of charging cycles and possibly damaging the structure.
  • Don’t exceed your amp limits.
  • Dispose of damaged batteries appropriately (check with your local council).
  • Keep batteries out of reach of children and pets.

Nominal Specification:

Battery Type Flat Top
Model IMR 21700V1
Rated Capacity 4000mAh
Nominal voltage 3.7v
Voltage at end of discharge 2.5v
Max charging current 4A
Standard charge 2A
Discharging current 30A
Charging temp range 0°C – 45°C
Discharging temp range 20°C – 75°C
Size 21 (±0.2) mm X 70 (±0.2) mm


Certified by CE, RoHs, MSDS and FCC

SKU: LUXEFST21700FLTOP40MAH Categories: , , Tag:
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