NEW YORK, NY - AUGUST 2: A Samsung employee demonstrates underwater use of a Samsung Galaxy Note 7 smartphone during a launch event for the Samsung Galaxy Note 7 at the Hammerstein Ballroom, August 2, 2016 in New York City. The stylus equipped smartphone will be available starting August 19, with preorders starting August 3. (Photo by Drew Angerer/Getty Images)

You plug your smartphone into the bedside charger and place it on your nightstand with care.You wake to find your nightstand in flames, smoke billowing everywhere Or maybe your Jeep. Your hotel room. Your entire home.

How could this have happened? Simple: your phone is a Samsung Galaxy Note 7 — and it’s one of over a hundred that have spontaneously burst into flames.

After 35 reported incidents of overheating smartphones worldwide, Samsung made the unprecedented decision to recall every single one of the Galaxy Note 7 smartphones sold. That’s said to be 1 million of the 2.5 million that were manufactured. (Since the recall was first announced, the number of explosive Note 7s has nearly quadrupled.)

The company stopped all sales and shipments of the Note 7, worked with government agencies and cellular carriers around the world to provide refunds and exchanges for the phone, and apparently it still wasn’t enough: As of October 10, as many as five of the supposedly safe replacement Note 7 phones have caught fire as well, and Samsung is asking all users to shut down their phones.

Once again, every US carrier has halted sales of the Samsung Galaxy Note 7, and a second recall may be nigh. We’re not sure why the new batteries might have caught fire, as Samsung told us they’d be brand-new.

But why did these phones even catch fire to begin with?

Here’s what we know about Samsung’s battery woes.
The basics

The science behind phone battery fires is actually pretty simple, and fairly well understood. Much like the infamous exploding hoverboards, phones use lithium ion battery packs for their power, and it just so happens that the liquid swimming around inside most lithium ion batteries is highly flammable.

If the battery short-circuits — say, by puncturing the incredibly thin sheet of plastic separating the positive and negative sides of the battery — the puncture point becomes the path of least resistance for electricity to flow.It heats up the (flammable!) liquid electrolyte at that spot. And if the liquid heats up quickly enough, the battery can explode. The Galaxy Note 7 certainly isn’t the first phone to catch on fire, or even the first giant recall. By 2004, a spike in cell phone battery explosions prompted this CNET article. In 2009, Nokia recalled 46 million phone batteries that were at risk of short-circuiting. Exploding phones have even killed people.

No brand or model is necessarily safe: for instance, unlucky iPhone owners allegedly suffered nasty burns from exploding devices in 2015 and 2016. And though the Galaxy Note 7 is making headlines right now, other Samsung phones have also burst into flames, like the Galaxy Core that allegedly burned a 6-year-old child earlier this week.

We’ve known for years that lithium ion batteries pose a risk, but the electronics industry continues to use the flammable formula because the batteries are so much smaller and lighter than less-destructive chemistries. Lithium ion batteries pack a punch, for better or for worse.