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Journey to an RDA - Battery types and safety - Part 1

Published by Nataani in the blog Nataani's blog. Views: 3639

In order for this to be a comprehensive guide I have decided to go through batteries in detail. It should be noted that there are plenty of great resources on the ECF which pertain to battery safety. Of note are Baditude's blogs.

1. What do all the numbers and letters mean?
2. ICR vs IMR
3. Battery failure
4. Avoiding battery failure
5. Long term battery life
6. Battery charge

1. What do all the numbers and letters mean?

In short – The numbers refer to the battery sizes, and the letters refer to the chemistry.

Size descriptors:
There are three main sizes of batteries that are used in mods; 18650, 18490 and 18350. The numbers are a reference to the dimensions of the battery. Height, and width.

The first two numbers are the diameter of the battery in mm, the three subsequent numbers are the height in mm.

An 18650 is 18mm in diameter, 650 mm in height.
An 18490 is 18mm in diameter, 490 mm in height.
An 18350 is 18mm in diameter, 350 mm in height.

Chemistry descriptors:
The two main types of batteries we use are ICR and IMR.

Each letter in the designation means something different:
I – Lithium-ion
C – Cobalt
M – Manganese
R – Rechargeable

C-ratings and mAh:
The C-rating of a battery refers to how much continuous output the battery can handle, as a function of mAh. mAh refers to how much charge a battery can hold.

The relationship is:
Maximum current output in amps = C-rating * mAh / 1000

So a 1600 mAh battery with a C-rating of 20 can output 20 * 1600 / 1000 = 32 amps.

2. ICR vs IMR

ICR batteries are generally cheaper, and have low C-ratings, thus they have low maximum amp draw. The cobalt chemistry that they use is the common chemistry used in lithium ion rechargeable batteries, including those in AA. Due to the relatively volatile chemistry used in cobalt based chemistry batteries, they often come with a PCB (printed circuit board) attached on one end of the battery. It is essentially a fuse for the battery, ensuring that the battery will never output more than it can handle. ICR batteries with a PCB are typically referred to as ‘protected’. It is highly inadvisable to use non protected ICR batteries!

IMR batteries are more expensive and have high C-ratings, as a result they are considered ‘high drain’, thus they have high maximum amp draw. The manganese chemistry that they use is generally considered much safer than cobalt, as a result they do not come with PCBs, nor require them.

3. Battery failure

When the maximum current draw of a battery is exceeded the results can range from a hot battery, to catastrophic pipe bomb style failure. What happens generally depends on how long the battery exceeded its maximum draw, and by how much.

To keep this relatively simple, we wont go into the way a battery works, ion movement, or any of that scarily complicated chemistry.

What is important is that once the maximum discharge rate of a battery is exceeded heat will start to build up in the battery. Since the battery is mostly liquid inside this excess of heat can eventually start to boil the liquid. Once the liquid boils it will cause a massive pressure rise in the battery. If the force exerted by this pressure is greater than what the casing can handle, the casing will fail, expelling the contents of the battery. The more the maximum rating of the battery is exceeded, the faster heat will build up and the quicker the battery will fail.

Lucky for us most batteries casings are slightly flawed, sometimes by design. This results in one part of the casing failing before the rest of it. So for example, the top may pop off, venting in just one direction. In cases where the entire casing can handle the exact same pressure, the whole thing will fail at the same time, like a pipe bomb.

4. Avoiding battery failure

Scarily, there are MANY reasons why a battery might fail.

a. Your build
If for example you build a 0.1 ohm coil, and use it with a battery whose maximum discharge rate is 10A, your build will try to draw 4.2 / 0.1 = 42 amps from the battery. This FAR exceeds the maximum draw of the battery, and will result in failure quite quickly.

b. Short circuit due to a bad build
If you have a short circuit on your build – when a lead is touching the deck, or a post, or wraps are overlapped, etc – the resistance of your coil will drop. How much it drops by depends on just what kind of short circuit you have. If the resistance drops to the point that the maximum amp draw is exceeded – battery failure.

c. Short circuit for other reasons
A great (or terrifying) example of this happened to a friend of mine. He simply tossed a battery into his inside coat pocket… with his keys. The keys connected the poles of the battery, creating a short circuit. He was lucky enough to feel the heat before anything catastrophic happened, he did the smart-ish thing and threw the battery in a snow bank. This was smart because it cooled down the battery rather quickly. Dumb because he handled the battery with his hands, and also because the lithium in the battery, if it vented, would react with the water in the snow bank.

Protip – Always store your batteries in a battery case!

5. Long term battery life

Over time batteries do degrade. This is because during the recharge process lithium is deposited in small quantities on the electrodes in the battery. Over time this can result in shorts or corrosion.

How many cycles you can put your battery through depends on many factors. But as a rule of thumb do not keep them for more than a year.

Factors that can reduce the life of your battery:
a. Extreme hot cold temperature changes
Avoid leaving your batteries in an overly hot or cold car. Keep them away from your heaters. This one is pretty self explanatory.

b. Over charging
Just like not all batteries are created equal, not all chargers are created equal. The best charger on the market at the moment is the Nitecore intellicharger.

c. Over discharging
Most batteries will simply stop firing when they reach a certain voltage (normally 2.7). This is not always the case though, discharging past this can also cause issues.

d. Too frequent charging
Every charge cycle your battery goes through can result in lithium being deposited. So, the more frequently you charge a battery, the less life you can expect from it.

The result of this, to maximise your battery life, is a rather delicate balancing act. You dont want to overcharge, nor overdischarge, nor charge too frequently. So you want to make sure that your charger does not exceed 4.2 volts, you also want to make sure you do not discharge past 2.7 volts. A good charger, like the nitecore, can read the voltage on your battery, helping you avoid this.

6. Battery charge

It is relatively easy to calculate how long your battery will last based on the mAh rating of your battery.

mAh is the unit for milliamp-hour This means the number refers to how many milliamps the battery can discharge at in order to discharge for a full hour.

So for example, a 3000 mAh battery can discharge at 3000 milliamps (3 amps) for one hour.

If you discharge at a higher rate than this, the math is simple to calculate how many seconds you can expect to get out of your battery with your current build:

seconds = (mAh rating / 1000) / (amps your drawing) * 3600

So for example, if you were to draw 9 amps continuously from a battery rated at 3000 mAh (which better be able to handle 9 amps!) you can expect:

(3000 / 1000) / 9 * 3600 = 1200 seconds = 20 minutes

I hope this all made sense, if you have any comments or questions feel free to leave them in the comment section and either I or some other knowledgeable person will surely answer you!

Happy vaping!
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