Vaping 101: Voltage Drop

Posted by Mitch Clarke on 21st May 2018

Voltage drop is one of those controversial topics highly debated by vapers all across the globe.

While it doesn't affect regulated mods nearly as much since those devices can simply increase the voltage to compensate for any internal resistance, voltage drop is the notorious enemy of mech mods everywhere, and for good reason!

These devices function purely off of the raw power provided by the bare-bones battery cell—any reduction in voltage is a reduction in precious power!

So What Is "Voltage Drop"?

Voltage drop is the reduction in the actual voltage output supplied by your battery to your installed atomizer compared to the resting voltage measured when the battery is outside of the mech mod.

Wikipedia has a pretty solid definition of voltage drop:

Voltage drop describes how the energy supplied by a voltage source is reduced as electric current moves through the passive elements (elements that do not supply voltage) of an electrical circuit. The voltage drop across the internal resistance of the source, across conductors, across contacts, and across connectors is undesirable because some of the energy supplied is lost (dissipated). The voltage drop across the electrical load and across other active circuit elements is essential for supply of energy and so is not undesirable.
Voltage drop - Wikipedia

This may be a little confusing at first, so let me give an example:

Say you have a battery reading 4.2V fresh from the charger and you install it in a mech mod with a 0.1Ω atomizer attached.

But your mech mod is hitting pretty weak, not at all like the plumage sent out by your regulated mod set to the same voltage.

So you have the idea to get the multi-meter you have laying around and hook it up to your mech mod to see what's going on—good idea!

You remove your installed coil and replace it with the leads of your multi-meter, carefully tightening them down in the posts of your atomizer.

You press the fire button and not to much surprise, you get a voltage reading nearly exactly the same as the resting voltage of the battery.


It would seem like what's going in should come out easy-peasy, just like it is now, but that doesn't seem to be the case for actual vaping situations.

So then, what if you want to test your mech mod under real world circumstances? Your mech's electrical circuit also usually has the atomizer installed in the pathway, so you may as well test it under those conditions to see what you're working with.

You then reinstall your coil and try the measurement again—keeping the meter leads in the postholes or pressing them against the posts—only to get a reading that's much lower than your first two measurements! What gives, man?

Well, what you just witnessed was the voltage drop caused by a combination of your mech's inherent resistance and battery sag under load, which is a lot like how it sounds: the battery voltage drops under the stress of pushing electrons through added resistance, delivering less power to your atomizer than theoretically possible.

So if you've been bragging to your friends about how many watts you've been hitting, I've got some bad news for you.

But what exactly is going on when this inconvenient phenomenon occurs?

How It Works

The way it works is actually relatively simple: the amount of voltage either sent to your coil or dispersed randomly is equally proportional to the resistance of your coils compared to the resistance of your mech mod plus the resistance of your battery.

For example, say you have a 0.4Ω coil installed on a mech mod with 0.015Ω resistance and a battery with a 0.005Ω resistance. That's a proportion of 0.4 to 0.02 (coilΩ : mechΩ + batteryΩ) or 20:1.

That means that the mech mod will provide ~95% (20/21th) of the battery's resting voltage while losing ~ 5% (1/21st) to voltage drop when it's set to power this particular mech mod setup.

Keep in mind, this value shifts as you increase or decrease the coil's resistance.

So if you were to use a 0.1Ω coil build with the same mech mod and battery (0.1 : 0.02), that's a proportion of only 5:1—only ~83% (5/6th) of your battery voltage would make it to your atomizer while the remaining ~17% (1/6th) would be lost to inefficiency.

What Voltage Drop Is Not

It's important to keep in mind that voltage drop isn't some arbitrary reduction in power decided by the mech mod alone.

The amount of voltage drop is entirely dependent on the resistance of the installed coils, the resistance of the mech mod, and the internal resistance of your battery.

So any claims of a certain model of mech mod having a designated quantifiable amount of voltage drop aren't accurate in the slightest unless the resistance of the build and the make/model of battery are provided as well (i.e. a 0.2V drop with a .4Ω build on an LG HB2, a 0.8V drop with a 0.1Ω build on an iJoy 5-Leg 20700, etc.).

And even then, that's the very least amount of information you can go on to get a very approximate answer since you don't really know how old the battery cell is, how clean the mech mod is, etc.

Thankfully, there's a battery-powered vape superhero who goes by the name of Mooch—you may have heard of him before from his long career of testing the batteries we use in our mechs and regulated mods in order to find their true discharge rating. He also happens to test for DC IR and puts it directly in the Rating Graphic of the tested battery.

Did You Know?

Image Credit Cadex Electronics

It's apparently common knowledge an increase in a battery's internal resistance as its recharged and discharged is what causes its gradual decrease in battery life, but contrary to popular belief, the internal resistance of batteries does NOT change significantly over time, meaning you can keep pushing your old batteries without worrying about an unnoticed decrease in the amperage limit, only in the overall capacity.

Why, Though?

So what causes this pesky occurrence?


Specifically, resistance where it shouldn't be.

Voltage drop is caused by the resistance in your mech mod's electrical circuit (supplied by something other than the coils) randomly dispersing electrons throughout the mech's body as they pass through rather than being sent straight along to the atomizer.

This extra resistance can be from the threads and contacts in the mech mod's chassis, which is why it's exceedingly important to keep your mech's threads and contacts squeaky clean.

Any built-up dirt, gunk, corrosion, or patina covering these crucial points is what prevents electricity from passing through uninhibited, raising the resistance and reducing the amount of voltage sent straight along.

The resistance is also added by the battery itself—every battery has an internal resistance that perpetuates the battery sag under load.

The exact value of his resistance can vary between different makes and models of batteries, and even as much as a 10% difference between batteries of the same model.

How To Test For Voltage Drop

So you want to test for voltage drop.

Why even bother, though?

Voltage drop is such a fickle thing—one little change in your vape setup and your comparative values go haywire.

It's like trying to compare wattages across coils, even if they measure at the same resistance: where 25W is plenty of power for a smaller coil, it's probably not enough for larger coils.

It's much more reliable to try calculating the internal resistance of your mech mod and battery in order to predict future voltage drop.

While these values may change over time as your mech gets dirty and cleaned, they will at least stay relatively independent of other variables so you can use it to compare between other mods you own.

It's relatively simple to measure the values you need.

All you need to do so is a reliable multi-meter—that's about it!

You'll need to find the resting voltage of the battery, the atomizer's resistance, the voltage of the battery under load when measured at the atomizer posts, and the voltage of the battery under load when measured at the battery poles.

So let's begin!

You'll need:

  • A Digital Multimeter
  • A Battery to test
  • A Mech Mod
  • An RBA w/ Installed Coil

And here's what you need to do:

  1. To start, measure the resting voltage of your battery—it's good to know where you're starting in order to know how far you're dropping—and record it for future reference.
  2. Then, measure the resistance of your atomizer and record this value.
  3. Next, insert your battery into your mech mod and attach your atomizer.
  4. Touch the leads of your multi-meter to the posts of your atomizer—if you're using a single coil, you can tighten down your leads in the actual post holes for convenience—and fire your mech mod. Record the reading that's displayed.

So we've found the resting voltage, the atomizer resistance, and the voltage at the posts—good job!

We can use these three values to figure out the total additional resistance your vape setup adds to your atomizer (battery internal resistance + mech mod chassis resistance).

Using the calculator to the left, enter the three values we do know, mirroring the Atomizer Voltage UL value in the Battery Voltage UL field.

Now all we need is the battery's voltage at the poles under load.

Unfortunately, you can forget measuring this directly, it's just downright impossible to get the access you need to both the positive and negative poles while the battery is inserted.


But there's several ways we can use that dreaded phenomenon called "math" (am I pronouncing that right?) to crunch numbers until we're sick of life get the answer we're looking for!

So what are some of these methods? sure you wanna know?

Did I mention there's math involved?

Ahh, alright, alright, let's just get down to business.

1. Getting Wired

The first method doesn't involve a mech mod at all!

Testing battary resistance with multimeter and atomizer
Source Atmizoo

What we'll be doing is attaching the battery to your RBA via wires (usually simple copper wires with a known resistance) and measuring the drop at the battery poles from there—with no mech mod chassis to block access, it's very easy to get the reading we need.

After calculating the resistance of your battery using this reading, you can subtract that resistance from the total resistance value we found earlier using the three values—this will leave the resistance of the mech mod chassis as the difference!

Or just use the calculator above to do all the maths like some kind of super high tech computer magic!

2. Google to the Rescue

The second method is by far the easiest, though it's entirely possible that you'll get a completely wrong answer through no fault of your own!

So what is this second method?

Nothing more than a little Google-fu, and I've already done, like, half the work for you.

You're so welcome =]

There's a few charts online just like the one in the link above that list the many different types of li-ion batteries and displays the internal resistance of each one.

This makes finding your mech mod chassis resistance as easy as a single subtraction problem, but the values you find may not be perfectly accurate or even close to the mark at all.

So do much research into your battery model—look for the manufacturer's spec sheet first (because the internal resistance is relatively stable over the course of its lifespan), then look elsewhere for a measurement from a third-party if that's not available.

3. Gear Up

The third method can be just as easy, though you'll probably need to pick up some equipment to do so.

Simply use a battery internal resistance checker to measure your cell's resistance, then subtract this value from your total resistance value. Easy-peasy.

I have a gut-feeling there's a fourth method involving swapping out different mechs and batteries then pre-calculus–ing your way to figuring out the values for each, but it seems like you'd need to know the resistance of either a mech mod or a battery off-the-bat—it's impossible to discover both at the same time.

Bright side, once you figure out the resistance for even one of your devices, you'll be able to figure out the values for all of your devices!

Once you figure out the mech and battery resistances, you can swap out one for an unknown mech or battery, then retest the setup and reapply the values in the calculator!

Keep in mind, these values are pretty much only relevant to you. You never really know if both of your original values were exactly correct, and this will shift your answers away from being precisely right, but they'll still be relatively correct in that you can use them to compare your different mechs and batteries to each other to find your most efficient setup.

How To Prevent Voltage Drop In Mech MODs

This power-wrecking phenomenon can be like an energy-draining phantom haunting your mech mod—so how can you exorcise your mech mod without calling in the priesthood?

Ridding yourself of this worrisome specter is actually surprisingly easy—all it takes is a good cleaning along with a drop of prevention!

Cleaning the contact points of your mech mod like your threads and your battery contacts will go a long way to reducing the resistance of your mech mod's chassis.

Following that cleaning with a light coating of lubrication from a dielectric or anti-seize grease at the contact points will not only help prevent oxidation and patina in the delicate threads of your mech mod, it will also help prevent harmful electrical arcing at the battery contact.

And for the absolute best performance, replace your battery cells at least a year, or ~300 recharge cycles, after you first started using them. It won't affect how hard your batteries push, but it will make a difference in how long it can push at that level.