The batteries in your device, if you are using external batteries, are typically 18650 lithium-ion batteries. The designation of the term "18650" is because the width of the battery is 18mm and the length of the battery is 650mm. Lithium-ion or li-ion, is a commonly used rechargeable battery material. It's in your cell-phone and laptop batteries; It's used in Teslas and cordless drills. Regardless of what they are in, they have the potential to explode if they are misused or abused. This blog post is designed to help you be safer and well informed but is not a full comprehensive guide. You are responsible for you own safety.
Don't Buy Batteries Online Without Doing Your Research
Not all 18650 batteries are created equally and a huge majority of them on the market aren't safe to run in a vaping device. So it's not a good idea to buy the cheapest highest mah battery you can find on Amazon without being able to confirm the amp limit of the battery. In order for you to be safe, you'll want at least a 20amp battery. It's a common occurrence that someone will come into the shop with a set of NCR18650B in their mod and tell me they bought them online because they were cheap and they bought them in the same online shop that sold them the mod so they figured they were safe. The NCR18650B, is a green Panasonic battery with an amp limit of 5. Which means they are only safe for a maximum of 21 watts. So please do your research before you buy your batteries. Mooch is an avid vaper in the community who works for the government researching batteries and tests batteries for us vapers in his spare time. He's an excellent source of information regarding what batteries you should be using. Google him.
General Guidance and Maintenance
Pull out and examine your batteries often. Notice if there are any tears in the protective coating on the sides as well as the top insulator ring. If you happen to come across the coating coming off bring them to the shop and we will rewrap them for free.
Make sure they don't have any weird spots on them which could be an indication of the battery venting. Stop using them if they have corroded in anyway. Notice if you smell anything. If they smell weird stop using them as this could be a sign that the battery vented.
If you have to take the batteries out of the device or need to transport them, do not put them with anything metal as they have a potential to short. So don't put them in your pocket with loose change or keys or the junk drawer.
If you are boarding an aircraft do not put them in your checked luggage as this could cause them to explode due to the lack of air-pressure. They will be safe on-board of a plane because the cabin is pressurized.
It is extremely unlikely that your device will ever fail in a catastrophic way. But it's worthwhile to know what to do in those situations. When a battery fails in this manner it gets extremely hot very quickly and will start to vent off a hot gas, making a hissing noise. If you suspect that your device is unusually hot try to get it in a tub, bathtub, or outside away from people as soon as possible. However, if you hear the batteries venting treat it like a live grenade and get it away from you immediately.
Running batteries in a two battery device
If your device utilizes more than a single battery then you must use a "married" set of batteries. Married meaning that: A: They are the same make and model. And B: They haven't been previously used in a device without their other half. A battery that has been too discharged and is continuing to be used has the potential to fail, ie explode. When you use an unmarried set of batteries your potential for this failure greatly increases because there is an imbalance between what the batteries hold.
Say you have two batteries both the same make and model but you've been using one of the batteries for a year. Over time the capacity of the battery will diminish with use. So the 3000mah battery that you've been using for a year might only now be 1800mah. So when you mix the old battery with the new battery you have a 3000mah with an 1800mah. After a few hours of vaping the 1800mah will be down to like 25% while the new battery is down to 65%. With continued use in this state, this imbalance will continue to increase until the 1800mah battery is completely depleted at which point it's likely to fail. On top of that, when you have two batteries, with a difference in voltage, the device will have a harder time attempting to output a consistent voltage to the coil. While most modern mods will be able to recognize the battery imbalance and will not allow you to hit them until you put in a married pair, it's not a good idea to throw batteries in the device unless you know they are married.
Mechanical Mods and Battery Safety
Almost all mod explosions that are reported on the news are mechanical mods. Mechanical mods, also known as mech-mods, are mechanical in nature, hence the name. This means that instead of relying on a circuit board with safety features to power your device, you are basically hot-wiring a battery to the atomizer or coil. A mechanical mod is fundamentally a metal tube with 510 threading and a pin that presses against the battery on one end, and a physical button that when pressed presses against the battery on the other end. A hybrid is the same thing but instead of having a pin that connects to the battery the atomizer itself touches the battery. Hybrids are especially dangerous because of this. If the positive lead of the atomizer isn't protruding very far it's possible that when you screw it down to the mod, the battery will touch the threads of the atomizer instead of the positive pin creating a hard short.
A short occurs when there is no resistance or very little resistance in the circuit. Current=Voltage/Resitance or I=V/R the lower the resistance the more amps you are pulling. As discussed earlier, batteries have different amp limits. In cases of shorts the only resistance is the material itself. So if you were to use an ohms law calculator and plug in 4.2v (fully charged 18650 battery) .02ohms (my guess at the resistance of a copper tube, but regardless of accuracy, it's an extremely low resistance for demonstration purposes) you'd find that you'd be pulling 210 amps from the battery.
To give more context about why one would use something so dangerous; Mechanical mods came out at a time when almost every atomizer was greater than 1.2ohm and most devices were going up to a maximum of 12.5 watts. The baddest chip on the market was the DNA 20 chip from Evolv that went up to a whopping 20 watts! Mechanical mods were necessary if you wanted a good vape, given the context of technology at the time. You'd use a RDA, rebuildable atomizer, and throw in a .3ohm build and get 59 watts out of it. Which, at the time, was pretty remarkable. But as soon as box mods became available mechanical mods were obsolete. A box mod has safety features and the ability to adjust wattage among many other things that a mechanical mod simply can't do.
I highly recommend against using a mech-mod. They do not hit anywhere near as good as a box mod and they are a ton more dangerous. I feel like they represent us terribly as a community.