Last fact-checked 22 October 2020 | Report a factual error on this article
If you don’t know your 21700s from your 26650s, or if you have no idea what the mAh number of a battery is, you’re not alone! For new vapers, nothing is more confusing than batteries.
We sell thousands of e-cigarette batteries every year, and most of our battery buying customers get confused by terms like ‘nominal voltage’, ‘max charging current’ and so on. It’s worth getting to grips with this vape battery jargon, because the more you know about the batteries you’re buying, the better your vaping experience will be.
The numbers and classifications might seem baffling at first, but it’s not too complicated once you get into it. In this battery buyer’s guide we’ll help you understand everything you need to know about the main types of e-cigarette battery and what all the different technical terms in the product description actually mean.
E-cigarette batteries can be dangerous if they’re used incorrectly. The temperatures inside an e-cigarette go far beyond the kinds of temperatures you’re likely to reach in a remote control, electric toothbrush or any other ‘normal’ battery-powered household device, so you need to take care.
Vape devices and components are well regulated in the UK footnote 1, and 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, and 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.
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, 21700s and 26650s.footnote 2
Here’s a quick table showing the differences between of each type of e-cigarette battery:
|Battery Type||Diameter ⌀||Length ⇤ ⇥|
The name of each battery matches up with its physical size. The first two numbers in the name match the diameter (in millimeters), 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.
If you know what size, voltage and capacity you need in your e-cigarette battery, you’re most of the way there, but 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:
You’ll find the mAh number on almost every battery product description on our site. mAh tells you how many ‘hours of power’ you’re going to get out of an e-cigarette battery. Most e-cigarette batteries have a capacity of anywhere between 2,000 and 4,000 mAh. You don’t hold the fire button down for the whole time you’re vaping — you usually just heat your coil for a few seconds at a time — so don’t worry too much if you can’t buy a battery with a massive mAh rating. You’ll still get a lot of vaping done on a 2,000 mAh battery.
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 3.7V.
The Discharge Voltage, also known as the Minimum Voltage, is the point at which you should stop using your battery and either recharge it or recycle it. If you continue to use a battery after its voltage has dipped below the stated discharge voltage, you risk damaging the battery. 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 box mod will often give a warning and/or cut out completely just before your battery reaches its discharge voltage.
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 Voltage. If you run your vape device below the discharge current, you should get a little bit longer out of each battery.
The Max Continuous Discharge Current tells you how many amps you can safely squeeze out of a battery … but all bets are off on battery life if you rely on this number. 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 much faster than someone vaping at or below the discharge current.
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 go beyond the max continuous discharge current, unless you’re a very experienced vaper with a solid understanding of electrical engineering.
The Max Charging Current just tells you the safe current that you can charge your batteries up 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 it 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 — see our full range of battery chargers here.
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 -20-60C). In the UK, where average temperatures rarely drop below 0°C or beyond 20°C footnote 3, you might think that -20-60C 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 (stay away from unregulated box mods), vape at a safe current, and go for a battery with a high temperature range if you’re in any doubt.
Safety Note: Bear in mind that, 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 Ohms Law article.
We hope this battery buyer’s dictionary comes in handy. If you’re still confused by anything, please please get in touch. We’ve sold a lot of batteries over the years, and I’m an electrical engineer, so you can rest assured that you’ll be getting good advice.
Stay safe and happy vaping!
Links & Citations
A helpful summary of how e-cigarettes are regulated in the UK can be found on the Gov.uk website at the link below:
The top-selling battery format in the past year was 18650, accounting for 87% of sales. 20700, 21700 and 26650 formats make up the remaining 13%. This covers our own sales in the period 1st October 2019 to 30 September 2020.
In the UK, for the climate period 1981 - 2010, the coldest average minimum temperature is 0.7°C (February) and the warmest average maximum temperature is 19.4°C (July). See the link below for more information: