Sub Ohm Vaping Safety

Vaping Sub Ohm

Vaping Sub-Ohm Coils

There is an incredible amount of information available for those who intend to vape at sub ohm resistances.  Much is this information is geared toward those who are very new at it, and so many of us who have been vaping this way for a while tend to skim through these quickly, or not read them at all, because we already know these things.

However, there seems to be a lot of misconceptions going around about how to sub ohm safely due to some gaps in our knowledge.  As a fellow sub ohm vaper with a bachelors degree in engineering, I wanted to clarify a few things that seem to be frequently misunderstood about how to vape safely.

This article is geared toward those who already understand the basics of sub ohm vaping with mechanical mods.  If you are new to this and have never read a safety guide on advanced vaping, please read this before you proceed.

Please note that my purpose in writing this article is simply to advise vapers and clear up some details.  It is not my business if someone wants to push the limits of what is safe – I only wish to make sure you know what you are doing.  It is one thing for someone to push these limits knowingly; it is quite another for someone to think they are playing it safe when they are really not.

Resistance and Current Limits

Minimum safe resistance

It seems to be very common for people to seek out batteries specifically for their high current ratings.  There is a very high demand for Sony VTC5 batteries primarily because of this, to the point where they tend to be sold out everywhere you look.

However, for the majority of sub ohm vapers, this high of an amp rating is unnecessary, and can even be misleading.  In fact, there is a very narrow window between vaping at 20 amps (A) and vaping at 30A, and unless your coil build happens to fall within this tiny window, 30A batteries aren’t going to be much more useful to you.

Let me illustrate my point.  We are all familiar with Ohm’s law: voltage equals current times resistance, or V = I*R.  With a little algebra we can find out what resistance we have at a certain voltage and current, R = V/I.  Using this equation we can find the minimum resistance we can build to given the current rating of the battery.

For all 18650 and 26650 batteries, the maximum voltage when charged is 4.2 volts (V).  Plugging this into the equation along with the max continuous current rating of the battery will give you the absolute minimum resistance you can build to without overstressing your battery.

For a battery rated at 20A continuous, we have R = 4.2V / 20A = 0.21 ohms (Ω).

At 30A, we have R = 4.2V / 30A = 0.14Ω.

The difference between these two is only 0.07Ω!  So unless you plan to build your coils to exactly 0.2Ω, that little bit of extra room isn’t going to help you a whole lot.  If you always build above 0.2Ω, you will do fine with a 20A battery.

Ohm meter inaccuracy

Notice I said 0.2Ω, and not 0.18 or any other resistance.  It is not generally safe to build below 0.2Ω, even with a 30A battery.  I say this because you have no way of knowing the exact resistance of your coils.  Even the most high-tech, expensive ohm meters have some inaccuracy, and most of us are not using those.

Chances are you check your resistance on a digital mod, or using one of those little black boxes made by Tobeco.  Some of you may even be using a calibrated multimeter.  No matter what instrument you use, you can’t expect it to be more accurate than ± 0.05Ω, and that’s being generous.

There are two major reasons ohm meters are innaccurate.  One reason is that the resistance we are trying to measure is extremely tiny.  The resistance we use is so low that it is often considered “no resistance” in other engineering applications.

Trying to measure the resistance of our coil builds is like trying to measure the width of something down to hundredths of a millimeter.  You can get some really sophisticated calipers to do that, but don’t expect the numbers to be 100% accurate.

The other major reason ohm meters are innaccurate is because our builds are so low that the littlest movement can change the resistance.  If you build your coils and check the resistance, then heat them, pinch them, tweak them, and wick them, check it again.  Chances are the numbers are going to be different this time, sometimes by a lot.  This isn’t because the ohm meter is “wrong” – it’s because you changed the resistance when you moved the coils.

You may also find that your resistance changes a little as you use the coils.  Or that the exact same build gives you a different reading on another atomizer, or that tightening the posts a little changes the reading.  Again, there is nothing wrong with your ohm meter.  Just touching it with your fingers can give you a different reading, because there’s resistance in your fingers.

So if you build a coil to exactly 0.20Ω, you can’t expect that to be spot on.  Your ohm meter may be a little off, or you may change the resistance accidentally by moving the coil a little.

A battery rated at 22A allows for a minimum build of 0.19Ω at max voltage, so you may assume that your 0.20Ω build is perfectly safe.  As I’ve demonstrated, that may not be the case.

If you use 20A or 22A batteries, your best bet is to never build below 0.25Ω, and even that is pushing it.  Personally I don’t build below 0.3Ω on those batteries.

When using 30A batteries, I believe you can safely build at 0.20Ω, but I wouldn’t try to build below that.

Amp ratings – continuous versus pulse

Many people say that they can build to very low resistances because they go by the battery’s pulse rating rather than the continuous rating.  It is rumored that batteries can handle a much higher current output because of the pulse rating.

This is false.

Continuous amp ratings are the maximum current that the battery can handle discharging over a very long period of time.  Pulse ratings, on the other hand, are the maximum amount of current the battery can discharge in a very short period of time.

The problem with pulse ratings is that there is no universally accepted standard for battery companies to test pulse ratings.  A pulse is simply defined as a discharge in a brief time window, but there is no way to know exactly how long that pulse lasted in testing.  A pulse time can be anywhere from a couple seconds all the way down to a fraction of a second – in theoretical mathematics, the time of a pulse is considered “infinitely” short.

How long do you hold the button down when vaping?  Try timing it – I’m willing to bet it’s somewhere between 2 and 10 seconds.  Did the battery factory time their pulse testing to accommodate that?  Probably not.

Since we have no way of knowing how pulse ratings are determined, it’s safe to assume they don’t apply to vaping.  It’s better to stick to the continuous amp rating.

Sub-Ohm Batteries


It is well known at this point that the safest batteries to use are “safe chemistry” batteries.  These include IMR and INR batteries, among others.  It is no longer recommended to use ICR or any other kind of battery for vaping.

The reason we use safe chemistry batteries is that, unless stressed in a very unusual way (such as being thrown in a fire), they do not explode.  When overstressed, these batteries will simply vent noxious gasses.

That said, if you use one of these batteries in a mod that has no venting, it will explode if it starts to vent.  That is because the gasses are released at a high pressure, and if the mod has no venting, that pressure will build up inside the mod and explode.

Your best bet is to always check new mods to make sure they have venting built in.  If you modify your device in any way, make sure that it still vents.

I know many of you know this, but I felt the need to bring it up due to recent events.

Efest batteries

There has been some controversy over Efest battery ratings and whether or not they are accurate.

It seems to me that all of this controversy can be traced back to one battery testing facility in Europe (note: you will need to translate the page).  They do quality work and I can’t fault them.  However, I cannot verify what they’ve found regarding purple Efest batteries because I haven’t found any other facility testing them and reporting the same results (if any of you know of anyone else who has done the same tests on these batteries, please let me know in the comments).

Also, Efest recently issued a warning that some of the purple Efest batteries being sold are counterfeit.  They say that most of these batteries are coming from China, and give detailed instructions for how to tell if they’re counterfeit.  They are now putting “anti-fake” labels on their batteries to differentiate them from the counterfeits.

Counterfeit batteries are a very serious issue because they may not even be safe chemistry batteries, so if you suspect your battery is counterfeit it’s best to stop using it.  Please note that this is not the same thing as a reputable battery company simply rewrapping someone else’s battery as their own (like Efest rewrapping Sonys), in which case the battery is still guaranteed safe and fully tested.

Buying safe batteries

Due to the proliferation of counterfeits, I highly recommend that you only buy batteries directly from reputable dealers.  If you cannot buy directly from the company, buy from a vapor store like Madvapes or a flashlight store (like, and know exactly which batteries you are willing to purchase before you even visit the site.

I recommend the following battery brands for sub ohm vaping, in no particular order:

18650, 20A-25A: AW, Efest, Sony, Samsung, LG, Panasonic, Orbtronic, MNKE, EH, Vamped, Subohmcell

18650, 30A or higher: Efest, Sony, LG, Orbtronic, MNKE, Vamped, Subohmcell

26650, 20A or higher: Efest, Sony, MNKE, Vamped, Vappower, KP Private Label (Kidney Puncher)

Batteries in pairs

There are now many mods available that accommodate two, or more, batteries at once.  There is a significant difference in performance capabilities between whether they are connected in series or parallel.

It is important that you always buy the pair of batteries used in the mod together, and always use them together and charge them together.  Any difference between them can lead to one battery pumping out more voltage than the other and becoming strained.

Batteries connected in series, or “stacked”, will retain the same current but double the voltage.  For instance, if you use two 20A batteries, you will still have a max current discharge of 20A, but you will have a max voltage output of 8.4V.  This is helpful if your goal is to maximize power, or wattage (W), without decreasing the resistance of your build.

In fact, this will increase your power by a lot.  Power is equal to the voltage times the current, or P = V*I.  If you use 20A batteries and build to the lowest resistance possible, your power from one battery at max voltage is 4.2V * 20A = 84W.  If you stack two of these batteries, however, your power is now 8.4V * 20A = 168W!  Many people who stack batteries find that they prefer building their coils to a higher resistance because of this.

Batteries wired in parallel will retain the voltage but double the current.  So now if you use two 20A batteries, you will retain a voltage of 4.2 but have a max continuous current of 40A.  This allows you to lower the resistance of your build.

If you pair two 20A batteries, your minimum resistance is now 4.2V / 40A = 0.11Ω.  If you pair two 30A batteries, your minimum resistance becomes 4.2V / 60A = 0.07Ω!

That’s about as low as it gets.  If you plan to build to extremely low resistances, I highly recommend buying a box mod that runs batteries in parallel.

Charging your batteries

Lastly I will briefly discuss battery charging.  Most of you know that it is crucial that you use a good quality battery charger; however, because of issues such as this I feel I must restate the point.

My best recommendations for battery chargers are Nitecore and Efest brands.  There are a lot of different chargers out there, but some of them are really not made well, and unfortunately that is one of the easiest ways to start a house fire. (See our review on the new Nitcore Digicharger here)

I must also advise that you never charge your batteries when you are sleeping or not home, that you always take your batteries off the charger as soon as they are fully charged, and that you plug your charger directly into the wall or into a surge protector (i.e. do not use an extension cord no matter how tempting it may be).

Safe Sub-Ohm Vaping

I hope everything I’ve discussed in this article clears up some of the questions you may have.  With everything we know about vaping and battery safety, it really is not hard to sub ohm safely.  All that takes is understanding how it all works.

As always, if you feel that I’m not right about something, please feel free to comment and let me know.  I’m always willing to correct myself if need be.

  • Wynne 11/08/2014

    Thank you for the great info Christina, you are such a good writer. 🙂 Next time someone asks me about batteries, I will definitely refer them to this.
    Ha, I wish I could have found one good article like this not so long ago, it would of saved me from a lot of confusion over which batteries to buy, or not buy. It seemed the more little pieces of advice I found to read, the more confusing it all became.

  • Eric 11/15/2014

    Hello! Absolutely fantastic article, beautifully written and great information! I actually would love to use your article on my website, would you mind if I did so? Of course I’ll give you full credit as well as posting a link to your website?

      • Eric 11/17/2014

        Absolutely! Thank you so much, I will send you a link when I post it!

  • Martin Clark 11/22/2014

    Christina, Thank you for this. Coming up on 11 months of vaping and while I’ve learned a good deal, I still have much to learn. I do my research but lets face it, when you go from ecigarettes with a blue tip all the way to a 28 mm dual coil Tbh on a 180 watt God Box, there is a steep learning curve. Don’t even get me started on blending and steeping DIY liquids. I appreciate your article a great deal.

  • Jim Patrick 12/05/2014

    Great advice to all new vapors I have a question, I purchased ipv mini with Atlantis .5 ohm coil
    Now my question is I will be using efest 18650 35amp battery is that a safe setup I will be using
    Thank you

    • Chris Tibb Miller 08/15/2016

      there are no 18650 batteries rated above 30amps continuous discharge, the chemistry does not exist even in 2016, you calculate using the continuous discharge not the pulse rating. in this case efest rewraps that 35 amp is not the cdc it would be the pulse putting the cdc at around 15amps not 35

  • Brad Likins 01/04/2015

    Very educational information in your article. I’ve been vaping for almost a year and I still feel like I am a beginner at times. You can never stop learning about what you think you already know. Knowledge is power and it always pays to keep learning more. Keep up the great work you do. You learn something new everyday! Thank you for the article.

  • yinshidan 01/30/2015

    Hi Christina. you write some great articles. I will like to ask if one is allowed to post these articles on my blog if I write the source of the article? Thank you very much. Regards Dan

    • Nathan 01/30/2015

      Christina is no longer writing for vaping Cheap but if your interested in re-publishing her articles please contact me via e-mail.

  • Daniel 03/02/2015

    I have a question. I accidentally put one of my batteries the wrong way in my tank crossing parallel box. They became really hot. I need to know what to do

    • Nathan 03/03/2015

      Well if you want to be super safe you may want to get new batteries. Otherwise just wait till they cool and then test them to see if they work, if they still work just be careful with them for awhile. They may be fine.

  • Swags 06/13/2015

    Thanks for the info! This guide is more geared towards sub ohmer using mech mods or mods with replaceable batteries, correct? In other words, one with an istick 50w or regulated mod and altantis v2 or some other sub ohm tank shouldnt have much to worry about in the context of whats discussed above, no?

    • Nathan 06/13/2015

      Yes this is more for mechanical mod use since with mechanical mods there is no restriction on ohm limits. Regulated mods will only work with coils above a certain ohm limit to prevent the problems discussed in the article.

  • William Thornley 07/04/2015

    Nathan, I can’t stress enough how much I enjoy your work. Even though I’ve only been vapeing since 2/14/15 I’m in deep! Also I haven’t smoked a single cigarette since my first vape! Wish it worked that well for everyone, and I smoked 40 years! Never dreamed I’d have a fascinating hobby AND be able to not smoke too. I can’t learn enough. I starve for information. We need sooo many more like you representing the vapeing community. Our enemies will use all these utube vapeing “stars” make us all look bad with their profanity and their stick it in the “man’s” face attitude. You sir, and others like you could help save this whole industry.

  • Seth 07/25/2015

    I’m using an Arctic Tank by Horizon Tech .2ohm coils BTDC on a black Tank Crossing unregulated Mod. I was wondering why am I not getting big clouds like everyone else is I also have an IVP2S Mod that I was running the Arctic tank on also. All I did was put the Arctic on the Tank Crossing and idk just doesnt seem to want to get a big huge cloud. Should I adjust the pin on the box? Should I not use this tank at all on this Mod box…I’m really frustrated!!! plz help

    • Nathan 07/25/2015

      You may want to try a new coil, sometimes you get bad coils that don’t work that good.

  • Chris 08/25/2015

    Hi, I’m using a avid lyfe with a tobeco turbo drip with aspire 1800 40A super high discharge batteries. I’m building my coils to 1.5 but after a couple of days I test them again and they are reading 0.07. Is this in safe tollerences with that particular battery and also is it normal for coils to drop lower after they have been used? Please help, thank you.

    • Nathan 08/25/2015

      I assume you mean 0.15 and dropped to 0.07. Your ok with the 0.15ohm coil on the 40amp battery but 0.07ohms is too low. Coils can change in resistance slightly but cutting the resistance in half means something is wrong.

  • rick 08/31/2015

    hmm my usual builds come out between 0.1 ohm to 0.15 ohm on a series box mod ( segelei 150) and i vape that between 60w-120w depending on my vape needs ( the higher wattage for when i need a good shot of nicotine to keep from raging lol) using samsung 25r batteries , youre saying keep my build above .3ohm ?

    • Nathan 08/31/2015

      This article is really about battery use in single 18650 mechanical mods with no regulation. Your using a dual 18650 regulated box mod so this information doesn’t really apply.

  • Thomas 10/04/2015

    I know this information might be irrelevant to me but it still expanded my knowledge on vaping and was easy enough to actually understand so thank you!

    but i was wondering if you could help me still, i have a smoke x cube 2 with a tfv4 quad coil running at 0.15ohm. The batteries I’m using are efest 18650 3.7v 35a. Is this safe and what is the chance of venting?

    Also my charger is a trustier tr001 which i’ve heard is really quite unsafe, could you confirm this?

    • Nathan 10/05/2015

      This article is about mechanical mods with single 18650 batteries. The Xcube is a regulated mod so its different. The batteries you are using will be fine. I have never heard of the “trustier tr001” charger so I can’t help with that.

  • Nate 11/12/2015

    Very helpful! I know a little about sub ohm vaping even tho it’s literally how I started vaping. I was using the VCT tank from Smok (which I highly recommend) and it wasn’t until later I started using RDAs and building my own coils. It’s turned into quite a hobby for me and I love learning stuff about it. I’m not going to pretend that some of the algebra stuff didn’t confuse me but that’s just because when things become difficult I start thinking about how much I love chocolate chip cookies. Sorry, I strayed there for a moment. Would it be okay to read some from this on a video for YouTube? I would be happy to link this website and give you full credit. And I’m also looking for people who like talking vape stuff to do some live videos, answer questions in the comments and talk about new devices, rdas, builds, stuff like that if anyone reading is interested. Just let me know. Thanks and wonderful article! 🙂

    • Nathan 11/13/2015

      Yes, you can read parts of the article as long as you cite as the source.

  • Joshua 12/13/2015

    So i’m interesting in sub ohm vaping, I was thinking about getting the UD Bellus dual coil RTA. Would it be safe to run using an unregulated Nemesis at .5 ohms with a single MXJO IMR 18650 3000mAh 3.7v 35a battery.

    I currently run a kayfun 3.1 ES with the nemesis with a kick and the same battery listed above and I want to upgarde.

  • Fred 12/14/2015

    Christina, you mention at the end of the article that high quality chargers are crucial. I’m very new to vaping, and I got a IPV4 kit with a Samsung INR 18650 -25R (2500 mAh 3.6v). The kit came with a small USB cable for charging. Is there a disadvantage to charging the battery INSIDE the mod, with the supplied USB cable? Would you recommend that I get an external charger right away?

    • Nathan 12/14/2015

      Christina no longer writes for us but I will answer your question. We always recommend an external charger when using 18650 batteries. You may have heard of exploding e-cigarettes in the news, well 80% of these happen when the device is charging. A high quality charger can also improve battery life and performance.


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