Don't know your 21700s from your 26650s? No idea what mAh means? You're not alone! For new vapers, nothing is more confusing than batteries.
In this simple buyer's glossary we'll help you understand everything you need to know about vape batteries. We'll explain the main types of e-cigarette battery, and show you what all the different technical terms actually mean.
Quick Links
- Why you need to understand battery jargon
- What's the difference between 18650, 20700, 21700 and 26650?
- 18650 vs 21700: Which should you choose?
- Battery buyers' dictionary
- Nominal Capacity (mAh) – What does mAh mean?
- Nominal Voltage
- Discharge Voltage
- Discharge Current
- Max. Continuous Discharge Current
- Pulse Discharge Current
- Max Charging Current
- Discharging Temperature Range
Every Vaper Needs to Understand E-Cigarette Battery Jargon!
E-cigarette batteries can be dangerous if they're used incorrectly. Vape devices and components are well regulated in the UK (see gov.uk), but they're powerful. If you're using a good box mod or vape pen you'll very rarely run into any sort of trouble. Still, you're carrying around a battery with enough power to light a small fire — the more you know, the safer you'll be.
A solid knowledge of how e-cigarette batteries work will save you money in the long run, too. If you're planning to vape for a long time, you can expect to go through a lot of batteries. You want to squeeze every last drop of efficiency out of the batteries you buy. One way to do that is to understand the different properties listed on the product description pages. That way, you can pick a battery that suits your device and style of vaping perfectly.
Understanding battery specifications helps you vape more safely and get better value for money by choosing the right battery for your device and vaping style.
What's the Difference Between the Different Types of E-Cigarette Battery?
E-cigarette batteries are all the same shape (cylinders with flat ends - they don't have a button terminal at the + end like an AA or AAA battery).
The most popular types of battery in the UK are 18650s, 20700s and 21700s. As of January 2026, 18650s outsell all other battery formats by a significant margin, and remain the industry standard for most vape devices.
Here's a quick table showing the differences between each type of e-cigarette battery:
| Battery Type | Diameter ⌀ | Length ⇤⇥ | Typical Capacity |
|---|---|---|---|
| 18650 | 18mm | 65mm | 2,000–3,500 mAh |
| 20700 | 20mm | 70mm | 3,000–4,200 mAh |
| 21700 | 21mm | 70mm | 3,000–5,000 mAh |
| 26650 | 26mm | 65mm | 4,000–5,500 mAh |
As you can see, the name of each battery matches up with its physical size. The first two numbers in the name match the diameter (in millimetres), and the next three numbers match the length (in tenths-of-a-millimetre).
This is why it's so important to get the right battery type for your vape device. If you get the wrong type, it literally won't fit in your mod.
Always check your vape device's specifications before buying batteries. Using the wrong size can damage your device or create a safety hazard.
18650 vs 21700: Which Should You Choose?
If your vape mod supports both 18650 and 21700 batteries (many modern vape mods include adapters), you might be wondering which is the better choice. Here's how they compare:
| Factor | 18650 | 21700 |
|---|---|---|
| Capacity | Up to 3,500 mAh | Up to 5,000 mAh |
| Battery life | Good | 30-40% longer |
| Size & weight | Smaller, lighter | ~10% larger, heavier |
| Device compatibility | Most vape mods | Newer mods only |
| Availability | Very common | Increasingly common |
| Price | Generally cheaper | Slightly more expensive |
| Best for | Most vapers, portability | High-wattage vaping, longer sessions |
When to Choose 18650
The 18650 remains the most popular vape battery for good reason. Choose 18650 if:
- Your device only accepts 18650 batteries
- You prefer a smaller, lighter setup
- You vape at moderate wattages (under 80W)
- You want the widest choice of batteries and chargers
- You already own 18650 batteries and compatible chargers
When to Choose 21700
The 21700 is becoming increasingly popular, especially among high-wattage vapers. Choose 21700 if:
- Your device supports 21700 batteries
- You vape at high wattages (80W+) and want longer battery life
- You're using a single-battery mod and want maximum capacity
- You don't mind slightly more weight and bulk
If you're currently using a dual 18650 mod and want to downsize, switching to a single 21700 mod can give you similar battery life in a smaller package.
E-Cigarette Battery Terms You Need to Know
As a minimum, you should know what size, voltage and capacity you need in your e-cigarette battery. There are other terms that you should familiarise yourself with, too. Here's a list of the terms you'll usually see when browsing our e-cigarette batteries department:
Nominal Capacity (mAh) – What Does mAh Mean?
mAh stands for "milliampere-hour" (sometimes written as "milliamp hour"). It's a unit that measures how much electrical charge a battery can store and deliver over time. In simple terms, mAh tells you how long your battery will last before it needs recharging.
Think of mAh like a fuel tank in a car. A bigger tank (higher mAh) means you can drive further before needing to refuel. Similarly, a battery with a higher mAh rating will power your vape for longer before it runs flat.
Here's how to understand the numbers:
- A 2,000 mAh battery can theoretically deliver 2,000 milliamps of current for one hour, or 1,000 milliamps for two hours
- A 3,500 mAh battery can deliver 3,500 milliamps for one hour, giving you significantly more vaping time
Most e-cigarette batteries have a capacity of anywhere between 2,000 and 5,000 mAh. You don't hold the fire button down continuously while vaping — you usually just heat your coil for a few seconds at a time — so even a 2,000 mAh battery will get you through a good amount of vaping.
| mAh Rating | Battery Life | Best For |
|---|---|---|
| 2,000–2,500 mAh | Half day (light use) | Low-wattage MTL vaping |
| 2,500–3,000 mAh | Full day (moderate use) | General everyday vaping |
| 3,000–3,500 mAh | Full day (heavy use) | Sub-ohm vaping |
| 4,000–5,000 mAh | Extended use | High-wattage cloud chasing |
Higher mAh = longer battery life. But there's often a trade-off: batteries with very high mAh ratings sometimes have lower discharge rates, which can affect performance at high wattages. Always check both the mAh and the amp rating for your vaping style.
Nominal Voltage (V, or Volts)
The Nominal Voltage is the "normal" amount of voltage that you can expect from your battery. A fresh battery might start out with a higher voltage than the nominal voltage, but as the power is drained from that battery over time, that voltage will naturally start to decline. Nominal voltage gives you a reliable "average" value that you can rely on for most of your battery's lifespan.
Most e-cigarette batteries run on a nominal voltage of 3.6V or 3.7V. A fully charged battery will typically read around 4.2V, dropping to around 3.2V when nearly depleted.
Discharge Voltage (V, or Volts)
The Discharge Voltage, also known as the Minimum Voltage or Cut-off Voltage, is the point at which you should stop using your battery and recharge it. If you continue to use a battery after its voltage has dipped below the stated discharge voltage, you risk damaging the battery permanently.
You'll usually notice the drop in voltage as your battery runs out — you'll get weaker vapour and less crackle. The safety chip in a good regulated box mod will often give a warning and/or cut out completely just before your battery reaches its discharge voltage.
Never discharge your battery below 2.5V. Most manufacturers recommend not going below 3.2V to preserve battery health and maximise the number of charge cycles you'll get.
Discharge Current (A, or Amperes)
Discharge Current is the "normal" current strength that you should run your battery at. In theory, if your vape device is running at the exact same number of amps as the discharge current of your battery, you will get the exact number of "hours of power" promised in the Nominal Capacity.
If you run your vape device below the discharge current, you should get a little bit longer out of each battery.
Max Continuous Discharge Current (A, or Amperes)
The Max Continuous Discharge Current (often called the CDR or amp limit) tells you how many amps you can safely draw from a battery continuously. This is one of the most important specifications for vapers, especially those who vape at high wattages or use low-resistance coils.
If you run your vape device at the same number of amps as the battery's max continuous discharge current, you won't be risking anything from a safety perspective, but you'll go through batteries much faster than someone vaping at or below the standard discharge current.
Common CDR ratings for vape batteries:
- 10-15A: Suitable for low-wattage, mouth-to-lung vaping
- 20-25A: Good for moderate sub-ohm vaping
- 25-30A: Ideal for high-wattage cloud chasing
Pulse Discharge Current (A, or Amperes)
The Pulse Discharge Current tells you how far your battery's manufacturer thinks you can push your battery in a single short pulse. We're a little uncomfortable with pulse discharge current, because a "pulse" isn't very clearly defined.
For instance, some manufacturers might consider a single split-second camera flash as "one full pulse", but vapers will often push and hold the firing button on their e-cigarette for three seconds or more.
Our advice is to never exceed the max continuous discharge current, unless you're a very experienced vaper with a solid understanding of electrical engineering. Ignore pulse ratings when choosing batteries for vaping.
Max Charging Current (A, or Amperes)
The Max Charging Current tells you the maximum current that you can safely charge your batteries at. Rechargeable e-cigarette batteries can't take energy in as fast as they put it out.
If you try to charge a battery at a higher amp rating than its max charging current, the battery won't charge any faster, but it will heat up and could become a fire hazard.
When buying rechargeable batteries, you should always try to match the charging current of your charging device. Some chargers have a switch or dial that allows you to set the charging current — this is useful if you have batteries with different charging specifications.
Charging at a lower current (e.g., 0.5A instead of 2A) is gentler on your batteries and can extend their overall lifespan, even though it takes longer.
Discharging Temperature Range
The Discharging Temperature Range is simply the temperature at which your battery will work safely. Most e-cigarette batteries have a discharging temperature range of between -20°C and +60°C (written as -20–60°C).
In the UK, you might think that -20–60°C is more than enough for us. In most cases it is, but just bear in mind that the internal temperature of a battery is likely to be much hotter than the external temperature when the battery is hard at work.
To stay safe, our advice is to:
- Always use a regulated box mod (i.e. one with a safety chip)
- Vape at a safe current within your battery's limits
- Choose a battery with a wide temperature range
- Stop vaping if your device feels unusually hot
Battery Safety Essentials
Before we wrap up, here are some essential safety tips every vaper should follow:
- Always use a dedicated battery charger rather than charging via your mod where possible
- Store batteries in a protective case — never carry loose batteries in your pocket where they could short-circuit against keys or coins
- Inspect your battery wraps regularly — if the plastic wrap is torn or damaged, either re-wrap the battery or replace it
- Don't mix old and new batteries in dual-battery devices — always use a "married pair" that are charged and discharged together
- Replace batteries when they no longer hold charge well or show any signs of damage
To vape safely, you need to understand voltage, current and resistance. Your battery needs to work safely with your heating coil. To learn more about coil resistance and how it affects your voltage and current settings, please read our Ohm's Law article.
Ready to Buy?
We hope this battery buyer's dictionary comes in handy. Now that you understand what all the jargon means, you can confidently choose the right battery for your vape device.
Browse our full range of vape batteries, battery chargers, and battery cases to find exactly what you need.
If you're still confused by anything, please get in touch. We've sold a lot of batteries over the years, and our team includes electrical engineers, so you can rest assured that you'll be getting good advice.
Stay safe and happy vaping!