Understanding E-Cigarette Battery Usage

Understanding E-Cigarette Battery Usage

You’ve been successfully vaping with your starter kit, or another e-cigarette that comes with its own protected battery…but you’re thinking of stepping up your vape game to a PV mod.

Pretty simple, right?

Pick out the mod your interested in, throw a battery in, top it off with a new rebuild-able atty, or sub-ohm coils, and your good to go.

Wrong…

If your plans are to start vaping e-cig mods, the most important thing to understand is Ohms Law, and how it affects the battery of choice.

Your battery is going to be the most important decision you make. Without an understanding of the inherent weaknesses, you could be setting yourself up for failure…in some cases, catastrophic.

I will attempt to familiarize you on how to read battery specifications, and how to determine what may be best suited for your desired setup.

This should in no way be an end-all, simply a guide to get you on the right path.

Batteries are dangerous, and as e-cigs become more prevalent, we see a growing trend where there have been failures; either from not matching the proper battery for intended use, or from using inferior chargers.

Never skimp on batteries, or chargers.

A battery is a means of storing potential energy. Simply stated, a means of supplying the required volts needed for your setup, for a specified period of time.

There are six aspects that need to be taken into consideration, when choosing a battery for a PV mod, especially an all mechanical one with no built in protection.

  1. Understanding Ohms Law and how to use it.
  2. Determining the Ohms of your cartomizer and atomizer.
  3. Determining Ampere output.
  4. Voltage output.
  5. Maximum continuous discharge rate and why it’s important.
  6. Rated mAh and how to approximate your battery’s life span before requiring a recharge.

Throughout this article, the following references to Ohms Law will be made:

  • I = current (amps)
  • E = voltage (volts)
  • R = resistance (ohms)
  • P = power (watts)
Understanding E-Cigarette Battery Usage

Mathematical Formulas Based on Ohms Law

Ohms Law, what does it mean?

Ohm’s Law defines the relationship between Voltage, Resistance, and Current, or: I = E / R. For our purposes, for any given two known variables, referencing the mathematical formulas associated with Ohms Law, we are able to determine the unknown variable.

The relationship between Voltage (volts), Ohms (resistance), and Amps (current) will be the main concern. More about Watts when we get into determining battery life of a variable voltage device before requiring a recharge.

Don’t Want The Math? No problem, go directly to the calculator.

Why would I even care about this?
For most, especially when vaping a mechanical mod, determining the output in Amps is very helpful when deciding on a atomizer or cartomizer. Understanding the Amps produced from your setup becomes simple using “Ohms Law”.

Determining the Ohms of a cartomizer /atomizer

When purchasing atomizers and cartomizers, their specifications are usually listed in rated Ohms. However, these ratings can deviate. To find this reading on our own, a multimeter is required. Especially if you are attempting to push your setup to the limits.

I have noticed quite a few people are purchasing a screw on Ohm meter for testing their cartomizers and atomizers. I recommend a true multimeter, as you have more flexibility. These can also be purchased rather inexpensively.

Rather than attempt to show you with pictures, I am including a link to a Youtube instruction. One thing I noticed from this particular person, and is lacking in some, he is subtracting the internal resistance of his leads.

This is the correct way.

Determining Ampere output

Constant
Battery = 4.2v
With a mechanical, or non regulated PV mod, your beginning voltage will be around 4.0-4.2v freshly charged.

Variables

  • Cartomizer = 2.0 Ohms
  • Atomizer = 1.5 Ohms
  • Cartomizer(2) = 3.0 Ohms
  • sub-Ohm coil = .05 Ohms

What Amps are you creating with the four different cartomizers and atomizers?

Looking at Ohms Law, we can deduct that the formula needed for this instance is (solving for Amps):

  • E/R = I
  • I = Amps
  • E = Volts
  • R = Ohms

After utilizing the Ohms Law functions, we are able to determine that our Amps will be the following:

  1. 4.2v/2.0 Ohms = 2.1 Amps
  2. 4.2v/1.5 Ohms = 2.8 Amps
  3. 4.2v/3.0 Ohms = 1.4 Amps
  4. 4.2v/0.5 Ohms = 8.4 Amps

As you can see, based on the criteria, the Amps are significantly higher, or lower depending on the cartomizer or atomizer chosen.

When utilizing a mechanical mod, this becomes especially important. If we exceed the maximum discharge rate of the battery used, it can lead to catastrophic consequences.

What do the calculated Amps mean?
When calculating the Amps in a particular setup, it is important to understand that all batteries are not the same. It is imperative to ensure that the battery of choice meets the demands of the setup chosen.

When utilizing an all mechanical mod, especially when going sub-Ohm, the need to ensure the battery’s maximum continuous discharge rate is capable of handling the requirements (Amps).

Voltage output, what does it mean?

The voltage output on most non-regulated PV mods is anywhere from 4.2v (fully charged), to 3.5v (requiring a charge).

It is important to note, even though your battery says 3.7V, when fully charged, it is more likely around 4.2V.

The above figures only relate to un-stacked mods, or single battery mods.

With variable voltage devices, the voltage can be boosted, or bucked to output voltages that are higher than the input voltage from the battery.

Read more about variable voltage.

Maximum discharge rate, what does it mean?

Some suppliers list a battery’s maximum discharge rate in Amps, and as long as your setup does not exceed it, you’re good to go. Never exceed a battery’s maximum discharge rate.

Example
AW IMR 14500
Max. continuous discharge rate : 4A

AW IMR 14500

With a maximum continuous rate of 4Amps, this particular battery is sufficient to power the 3.0, 2.0, and 1.5 Ohm cartomizer/atomizer from above. However, it is not sufficient for use with the 0.5 Ohm, as that setup will output 8.4Amps, exceeding the max. of 4Amps by over two times.

What if there is no Amp rating listed?
If there is no Amp rating, we need to refer to the “C” listing.

In describing batteries, discharge current is often expressed as a C-rate in order to normalize against battery capacity, which is often very different between batteries. A C-rate is a measure of the rate at which a battery is discharged relative to its maximum capacity.

Understanding the “C” Rating
My main batteries are IMR 18650 3.7V 1600mAh, and their rating is listed as: Max. continuous discharge rate : 15C

AW IMR 18650

Converting C-Rating’s to Amps:

  1. Determine the Ah of your battery: 1600mAh / 1000 = 1.6
  2. Multiply the C-Rating by your battery Ah: 15 x 1.6 = 24Amps

In this example, the battery is more than capable for the required 8.4Amps output of the 0.5 Ohm atomizer/cartomizer.

What if the C-Rating is C/2?
Instead of multiplying our battery’s Ah value, we instead divide it by the C-Rating.

In this example:
1.6 / 2 = 0.8Amps

If we had a maximum discharge rate of 0.8Amps, it would be insufficient for any of our examples above.

Rated mAh, what does it mean?

mAh is the measurement of a battery’s storage capacity in “Milliamps Hour”, and is an indication of how long a battery will last between charges.

Don’t want the math? No problem, go directly to the calculator.

For example, to determine approximately how long a 1600 mAh battery will power a 3.7 volt device with a 3.0 Ohm cartomizer.

Formula and Estimation
Battery life = (Battery Capacity in mAh / Load Current in mA) x 0.70 x 3600

Battery Capacity
This is the easy part, and will be listed on your battery, or in its spec. sheet. In this example, 1600 mAh.

Load Current Calculations
To get the load current input, we look to Ohms law. Because we know the voltage and resistance (Ohms), we can solve for Amps.

  • E = I/R
  • Amps = Voltage/Ohms
  • Amps = 3.7/3.0
  • Amps = 1.23

Next, multiply 1.23 by 1000 for our final calculation, which results in 1230 mA (milliamps).

Example Input Calculations

  • Battery Capacity = 1600 mAh
  • Load Current = 1230 mA
  • Efficiency Loss = 0.70
  • Hour to seconds conversion = 3600

Calculations
1600 / 1230 x 0.70 x 3600 = 3278 seconds of battery life.

To approximate how long this particular setup will last before having to recharge the battery, we will next:

  • Determine how many seconds an average inhale lasts.
  • Divide the result from above by this number.

In this example, lets use 4 seconds as our average time for inhaling.
3278 / 4 = 819

Battery life in this example will be approximately – 819 4 second inhalations.

Another Example

  • Battery Capacity = 750 mAh
  • Voltage = 3.7v
  • Atomizer Ohms = 1.8
  • Load Current = 2055 mA
  • 750 / 2055 x 0.70 x 3600 / 4
  • Result = 230 4 second approximate inhalations

The previous examples are approximations only, and are not taking into consideration if you are vaping a variable voltage device. In order to determine an approximate battery life while utilizing a variable voltage mod, there is another step to take into consideration.

The law of conservation of energy states that power in (watts) must equal power out.

Referring to Ohms law, if we were to derive our load current based on volts and Ohms like in the previous examples, our calculations would be incorrect.

Instead, when taking into account for a variable voltage device where our voltage output is greater than the voltage input, we must take additional steps in our calculations.

Example Where Voltage Output is Greater than Input

Constants:

  • Battery Capacity = 1600mAh
  • Voltage (in) = 3.7v
  • Cartomizer = 3.0 Ohms

Variables:

  • Voltage (out)
  • Amps
  • Watts

To illustrate, lets first look at what our load current would be if we set our device at 5.0v output, solving for Watts.

  • Voltage (out) = 5.0v
  • P = (E x E)/R
  • Watts = (Volts x Volts)/Ohms
  • Watts = (5 x 5)/3.0
  • Watts = 25/3
  • Watts = 8.3

Load Current Calculations

  • P/E = I
  • Output Power (watts) / Input Voltage = Amps
  • Watts = 8.3
  • Load current = watts/input volts
  • Load current = 8.3w / 3.7v
  • Load current = 2.24 Amps

Solving for battery life with a variable voltage device:

Battery life = (Battery Capacity in mAh / Load Current in mA) x 0.70 x 3600

  • = 1600 mAh / 2240 mA x 0.70 x 3600
  • = 1800 approximate seconds
  • = 1800 / 4 second inhalations
  • = 450 approximate inhalations

Lets do one more for good measure.
Constants:

  • Battery Capacity = 1600mAh
  • Voltage (in) = 3.7v
  • Cartomizer = 1.8 Ohms

Variables:

  • Voltage (out)
  • Amps
  • Watts

To illustrate, lets first look at what our load current would be if we set our device at 4.0v output, solving for Watts.

  • Voltage (out) = 4.0v
  • P = (E x E)/R
  • Watts = (Volts x Volts)/Ohms
  • Watts = (4 x 4)/1.8
  • Watts = 16/1.8
  • Watts = 8.9

Load Current Calculations

  • P/E = I
  • Output Power (watts) / Input Voltage = Amps
  • Watts = 8.9
  • Load current = watts/input volts
  • Load current = 8.9w / 3.7v
  • Load current = 2.41 Amps

Solving for battery life with a variable voltage device:

Battery life = (Battery Capacity in mAh / Load Current in mA) x 0.70 x 3600

  • = 1600 mAh / 2410 mA x 0.70 x 3600
  • = 1673 approximate seconds
  • = 1673 / 4 second inhalations
  • = 418 approximate inhalations

Comparing the results from our variable voltage and basic 3.7 mod, there is a clear drop in battery life.

  • From 819 down to 450 inhalations
  • From 819 down to 418 inhalations

…a 45% and a 50% drop in approximate battery life before requiring a recharge.

Don’t worry if this seems confusing at first. Use the Ohms law wheel for reference, and practice with different builds.

Hopefully, this guide will help in getting acquainted to battery usage in PV mods. This is just a brief introduction, and is not complete, or all inclusive. Understanding the effects our choices with batteries and cartomizer/atomizers have is very important, and should not be taken lightly, or haphazardly.

Resources For Further Reading:
Battery University
Great Resource on Batteries
Understanding Ohms Law
Relationship Between Voltage, Current and Resistance
Understanding Low Resistance High Resistance Battery Life