note 7 burn explode

One of the at least 35 Note 7 units that caught fire or exploded

Every now and again we hear unfortunate stories about gadget batteries catching fire and even exploding (a term that is often used even for incidents that are less dramatic), sometimes causing harm to the unsuspecting user. While very rare, Samsung has been forced to recall its latest Galaxy Note 7 smartphones after concerns were raised that a small number of its handsets are shipping with defective batteries that may explode. Once again, dangerous lithium-ion batteries are back in the spotlight, but what actually causes a battery to go haywire?

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Causing explosions

Lithium-ion batteries seldom bulge or explode, but when they do, there are two leading causes. The first is a puncture, which might be caused by dropping your phone. A break in the thin compacted battery material between cells can produce to an internal short circuit, leading to swelling and potential explosions. Alternatively, cheaper batteries can sometimes accidentally feature rare microscopic metal particles inside that might come into contact with other parts of the battery cell, also leading to a short circuit.

With the Galaxy Note 7, Samsung and various reports suggest that the issue is caused when the device is charging, which leads us to our second major cause – heat. Excessive heat can again cause again internal short circuit within the battery, by breaking down the internal cells. However, this only usually occurs at very high temperatures, unless the battery is faulty. Overcharging may also be an issue, which is caused by batteries receiving more current than they can safely handle, causing them to overheat.

Too much heat in one area of the battery can lead to “thermal runaway”.  This happens when an area of a battery can’t cool down quickly enough, resulting in a breakdown chain reaction that generates more and more heat. In other words, excess heat causes a reaction that accelerates the temperature increase. Eventually, this can lead to a fire or explosion.

Typically, high-quality batteries will include safety features that can usually prevent this dangerous reaction from taking place. However, Samsung has stated that it has purchased battery packs from multiple providers, and perhaps some of these are more prone to failure than others.

Charging and heat

There are a number of potential causes of excessive heat in and around the battery in a modern smartphone. The move towards fast charging technologies is now forcing additional current into lithium-ion batteries, and with every power transfer there is always some heat generation. The more power, the higher the potential heat. While some of this heat-loss will occur at the battery itself, some heat will also be lost in the fast charging power conversion and power management circuitry, which is usually located next to the battery. This could certainly cause more heat at one end of the battery than the other.

The processors inside today’s smartphones are also producing more heat than the handsets from 3 or 4 generations ago. While not usually nestled next to a battery, this could further add to the temperate inside a modern smartphone, making it more difficult for heat to transfer away from the battery area.

We should be clear though that Samsung has indicated that it is the batteries that are at fault in the Galaxy Note 7 and not any other part of the handset. It seems unlikely that the Galaxy Note 7 has be built in such a way that it is producing too much heat that makes it unsafe to stick a battery inside. Instead, it’s more likely that just a small percentage of the batteries that Samsung has purchased are not coping properly with the heat produced or current provided while charging. Either by not matching up to the required charging specifications or by simply coming from a faulty batch.

Protecting yourself

Without knowing exactly what is causing issues with Samsung’s Galaxy Note 7, we can’t say precisely how to avoid potential problems. However, there are some general tips to follow that can help protect yourself and your device from catastrophe. General warning signs that your battery is damaged and could explode include a hissing sound, popping, or swelling.

  • Stop charging your phone it if becomes too hot. Allow your phone to cool down before charging it again and make sure that you don’t cover your phone to let heat escape properly.
  • Stick to first-party chargers. Use the charger included in the box to make sure that your phone is receiving the optimal voltage and current. If you’re using a phone with a USB Type-C port or Quick Charge, it might be wise to stick with the cable that came in the box too.
  • Don’t charge your phone in bed. I know it’s very tempting to watch a video or read before you fall asleep, but you don’t want to roll over on your phone and have it overheat. Not to mention that leaving your phone under a pillow while it charges will cause it to heat up.
  • Be mindful of where you charge your phone. Avoid charging for long periods of time in really hot places, such leaving your phone on a car dashboard, next to a radiator, or in direct sunlight on hot days.

If you do happen to notice your battery swelling, unplug your phone and remove the battery, but only if the battery is user removable. Don’t attempt to dispose of the battery or device in the trash. Always get rid of your batteries at authorised disposal facilities or some electronics retailers, such as Best Buy, that offer battery recycling services.

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If your battery and/or device is damaged as a result of a swollen or exploded battery, take your device to the retailer that you purchased it from or get in contact with the manufacturer. A replacement battery or device will usually be issued, especially if you have a warranty.

Robert Triggs
Lead Technical Writer at Android Authority, covering the latest trends in consumer electronics and hardware. In his spare moments, you'll probably find him tinkering with audio electronics and programming.