With battery power comes battery responsibility
Battery Specs and Their Implications
The batteries we use in electronic cigarettes are Lithium batteries, more specifically, Lithium Ion (Li-Ion) and Lithium Polymer (Li-Po) cells. While there are differences between the two, they are meaningless to a user, they are identical in every aspect that matters where safety is concerned.
Lithium Batteries have some basic specs that will matter. Namely their voltage output, capacity and most importantly, their Amp limit. Here’s a quick overview of these:
Voltage Output: This one is easy, as it is the same for all lithium cells. They are typically labeled as having a nominal voltage output of 3.6 or 3.7V. This is its average output, not its maximum one. These batteries are fully discharged at 3.2V, and fully charged at 4.2V. This matters where charging is concerned: if you discharge a cell below 3.2, or charge it above 4.2 internal strain and damage are likely to occur, subsequently making your battery much more prone to failure. Most regulated mods cut off your power before under-discharge happens. But with a mechanical mod, it’s on you to keep an eye on your battery level. This is also why it matters to invest in quality battery chargers, the good ones cut off charge at exactly 4.2, whereas this isn’t quite so sure with cheaper chargers.
Capacity: Capacity is calculated in milliamp-hours (mAh) and is a measure of how long it will last which will of course vary depending on the amount of power you are drawing from it. The only real concern here is in relation to selecting a charging speed. I usually recommend people charge batteries at a maximum of 50% of their capacity. For instance, if you wish to charge a battery at a speed of 1Amp, then you need to make sure your battery has a capacity of at least 2000mAh (which works out to 2Amp hour). If you’re going to charge a battery at 0.5A, then it needs to be at least a 1000 mAh battery… You get the picture. Charging a battery too fast is not a massive risk of explosion in and of itself, but it does wear the battery out, shorten its lifespan as well as make it more prone to other forms of harsh failure.
Amp Limit: This is the big one. Different batteries will have different amp limits. The amp limit is how much current (in amps) can be drained from a battery at a time without it failing. This is largely immaterial with modern-day regulated mods, as they have built in safety systems preventing the mod from firing if too much is asked from the battery, and overheat protection to cut off power should a battery heat up for any reason. But in a mechanical mod, this is paramount. Your hands and face depend on it.
Before we go any further, we need to examine ohm’s law. It is the formula behind how voltage, amperage and resistance relate to each other.
Here are the different elements used in ohm’s law:
P: Power (Watts)
E: Potential (Volts)
I: Current (Amps)
R: Resistance (Ohms)
Now Ohm’s law will be a differently reduced formula depending on the variable you need to know. I’ve included a pie chart of all the possible iterations of ohm’s law. But the variable we are concerned with here is I (current in amps). When you are using a mechanical mod, you need to know how many amps you will be drawing from your battery to insure your setup falls within that battery’s amp limit.
Here is the formula you’ll need:
Now we already know a full battery pushes 4.2 Volts. Supposing you’re using a 0.5Ω coil.
So you’re drawing 8.4 Amps from your battery, so you need a battery that has an amp limit of at least 10 amps (because it’s unwise to push the maximum limit of the battery). Now if you don’t want to bust your chops with math, there are multiple ohm’s law calculator smartphone apps available for free.
If you’re using multiple batteries it is important to know if they are in series or in parallel.
Series: In series, multiply the battery output voltage by the amount of batteries. For instance, two batteries in series will push 8.4V when full. Note that the amp limit will remain the same. If you stack batteries in a tube mod, they will be in series. And this is why it is dangerous to stack batteries. The compounded voltage puts tremendous strain on their amp limit, often resulting in catastrophic failure.
Parallel: Here, the voltage remains the same, but it is the amp limit that will be multiplied by the amount of batteries. So suppose you have two 30A batteries in parallel, you end up with 60A of limit. Parallel mods are often the way to go if you want to run very low resistance builds on a mechanical mod.
The last thing to know, is that having multiple batteries in a device can put various kinds of strain on their chemistry, so a few precautions need to be respected. If you’re using a mod with say two batteries, you need to use new batteries and marry them together, meaning they are never used individually. They must be used as a pair and charged as a pair treating them like they are a single battery. Not doing so can lead to uneven discharge or overdischarge of the cell(s), which can in turn potentially lead to catastrophic failure.
Most of us already know not to store batteries in excessive heat or cold. So barring the obvious, it is extremely important to carry loose batteries in cases. If conductive materials create a contact between both poles of the battery (such as a loose battery in a pocketful of change), it will short out, potentially causing it to vent or explode, which is not a desirable event in one’s pocket.
Continuous vs. Pulse
Batteries will often have multiple amp ratings. One for continuous current: this is its limit if one would discharge it continuously from full to empty. This one is a nearly absolute value. It is important to note that the amp limits advertised for batteries often aren't their continuous current output ratings.
The one that generates confusion is the pulse rating. Usually higher than the continuous rating, it represents the amp limit if you’re only pulsing the battery. The question is: How long is a pulse? Unfortunately definitions vary, and the only way to be sure is to find the datasheets for batteries which usually contain a graph of testing plotting a curve of how much amps can be drawn from a battery relative to the length of the pulse. Without their respective data sheets, pulse amp ratings are largely confusing at best and misleading at worse. I simply recommend you keep to a battery’s continuous discharge amp limit, as it is as close to an absolute value you are likely to get.
So that just about covers it.
Should you desire to dig more in depth than this simplified overview, there is a great website for that: batteryuniversity.com
Cheers and vape safe.
- Betsy Lipes