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There are a number of news stories like this (in Russian) of an iPhone 5 burning up and causing a fire while charging overnight, seriously damaging the owner.

There's another story going around of a girl dying because she was listening to her headphones overnight while the phone was charging, whereupon the phone unexpectedly ignited.

These stories seem slightly far-fetched to me (the girl in the image seems to have injuries that couldn't be caused by headphones), and the sources for them don't seem particularly reputable. Is there any credible risk of leaving your phone charging overnight or dying because of listening to music on your headphones while the phone is charging?

Peter Olson
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  • I don't know about the examples you listed, but one thing I would investigate is whether extension cords were involved in these incidents. "[A man fell asleep with his iPhone charging in bed. It nearly electrocuted him](https://www.washingtonpost.com/news/the-switch/wp/2017/04/01/a-man-fell-asleep-with-his-iphone-charging-in-bed-it-nearly-electrocuted-him-to-death/?utm_term=.4c1af75dd8a8)" (*Washington Post,* April 1 20017) mentions this as a factor (he was actually electrocuted by a metallic necklace he was wearing that contacted an extension cord in his bed) – paradisi Jun 26 '17 at 18:39
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    Lithium ion batteries have a chemestry that contains a huge amount of energy, and under certain failure modes they can release both a lot of heat and hydrogen gas. There is a non-zero risk of them exploding or catching fire (aka "thermal runaway") but that doesn't make them dangerous as such. If the device, the battery and the charger are good quality and in good condition then the risk of failure is extremely remote. – GordonM Jun 26 '17 at 18:46
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    @GordonM That's addressed in another question: [Can Lithium Ion batteries explode or self ignite?](https://skeptics.stackexchange.com/q/30615/37236) In fact, the answer lists "overcharging" as one cause, which might also answer this question. – Laurel Jun 26 '17 at 19:14
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    Does the fact that there have been billions and billions of overnight charges of smartphone without fire give you an idea of the answer? – DJClayworth Jun 26 '17 at 23:18
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    "Dangerous" is a vague term, and is going to lead to unsatisfactory answers. Let me invent some numbers. If 1 in 10 million charges results in "thermal runaway" and 1 in 10,000 of those causes a serious injury, we would have exactly this situation: anecdotal reports of people getting hurt and engineers reassuring us that it is safe. Both are right. – Oddthinking Jun 27 '17 at 02:10
  • Don't put your phone under your pillow while charging it. Apparently heat is dangerous..... –  Jun 27 '17 at 18:52
  • One detail is that prolonged charging increases the risk when a charger is "slightly" defective -- ie, tends to overcharge slightly. Repeated "slight" overcharging increases the likelihood of catastrophic battery failure. – Daniel R Hicks May 29 '18 at 12:26
  • Some news stories (perhaps not these) about bad thing happening when charging turned out to involve cheap non-approved charging systems. – GEdgar May 29 '18 at 13:22

3 Answers3

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Lithium batteries are based on a chemistry that can fail in combustive fashion. To avoid this, elaborate safeguards are in place to avoid those exact failure modes.

A defective battery can still self-ignite, though.

This can happen in a variety of ways. The electronics avoiding overcharging could be damaged. The battery could be physically damaged. There could be a construction defect.

Generally speaking, overnight charging or overnight use is no more dangerous than daytime charging / use. Yes, you might be asleep, but at the same time the environment is very quiet, and you are more likely to be alerted to a violently exothermic reaction happening on your nightstand than during noisy daytimes.

Factoring in all the failure modes that are more likely to happen at daytime -- your phone falling down, the battery being bent or pierced by something etc. -- charging your phone overnight is no more dangerous than charging, using, or carrying it at day.

DevSolar
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  • The two significant differences between night and day are that overnight charging is generally for 6-8 hours, vs 3-4 for daytime, and you are more apt to be inattentive at night. – Daniel R Hicks May 29 '18 at 12:24
  • @DanielRHicks: Once the phone is charged, the charging stops. And while you're more attentive at day, usually you are *using* your phone during the day as well.... – DevSolar May 29 '18 at 12:26
  • But does the charging stop when the phone is 95% charged or 103% charged? And, once charging "stops", does the charger still "trickle" a charge, or does it "wake up" every so often and check things by attempting to charge further? – Daniel R Hicks May 29 '18 at 12:35
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    @DanielRHicks all of those questions are answered by the engineering team, who built the thing to be as safe as humanly possible. The only way the answer can be something negative is, as pointed out in the answer, something in the device is damaged. – Erik May 30 '18 at 05:51
  • @Erik - It's all a matter of probabilities. The engineers set up things so that the phone *probably* won't catch fire. If it were "as safe as humanly possible" it would be encased in inches of asbestos insulation (oops, asbestos is unsafe) and would have a built-in fire suppression system. The engineers balance cost, marketability, and convenience (with a thumb on the scale in favor of cost). – Daniel R Hicks May 30 '18 at 12:19
  • @DanielRHicks right - but all of your probabilities are summed up by "the device is broken", since they all revolve around the device not working according to the design specs. – Erik May 30 '18 at 12:23
  • @Erik - Except that you don't know that it's "broken" until it catches fire. – Daniel R Hicks May 30 '18 at 12:43
  • @DanielRHicks: I believe I covered both the various failure modes (of which "problem due to charging" is but one) and the failure environments (of which I consider "in my pants", "in my hands" or "on my desk" to be *at least* as dangerous as "on my nightstand"). What is your suggested improvement to my answer? Or are you just chatting? – DevSolar May 30 '18 at 12:51
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No. The module that controls the rate of charge and whether any charge is drawn from the power source and the AC power adapter resides in the iPhone, itself. As such, it's really not possible to "overcharge" a modern smartphone.

Popular Mechanics says that lithium-ion batteries don’t overcharge, and instead will “trickle charge.” This happens when the battery reaches 100% and the charger vastly slows down the voltage that it sends to your iPhone, just enough to keep it charged up without overcharging.

GottaBeMobile: Can you leave your iPhone charging overnight?

This process charges the battery as quickly as reasonable while protecting the battery from damage or increased wear and tear. Please note that the charging IC - or Power Management IC - is located inside the iPhone. So this applies regardless of the external USB powering device you use to charge it.

When the battery is full, the charger turns off the charging process. The battery is left alone without current going into or out of it. This is because most Lithium chemistry batteries don't like trickle charging (a process you may hear from others where a constant voltage and low current is applied to a battery all the time to keep it topped off).

Charging ICs therefore turn the current completely off and power the phone itself from the charger. This is the only time the battery isn't charging or discharging - when it's full and the phone is plugged in.

..... Conclusion: The phone and its battery, therefore, will suffer absolutely no damage being plugged in for days at a time.

StackExchange AskDifferent: Is charging iPhone all night harmful to my iPhone?

Now, these references are specific to the iPhone, but the technology (despite Samsung's previous battery issues) is similar or equivalent between most modern phones.

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PoloHoleSet
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    You are describing the proper operation of lithium batteries. Cheap electronics may have a problem with shoddy ICs. Both links discuss if leaving it plugged in is bad for your battery. Neither link discusses catastrophic problems caused by overcharged Li-ion batteries, which is what the question asked about. – BobTheAverage Jun 26 '17 at 21:03
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    @BobTheAverage - read it again, Bob. The question asks if leaving the phone plugged in will lead to overcharging. It specifically refers to a story about an iPhone. Not sure why you think links that state that leaving an iPhone plugged in will not lead to overcharging is not relevant to a question asking if leaving a phone plugged in (with iPhone specifically mentioned) is dangerous. This is exactly answering the question, as asked. – PoloHoleSet Jun 26 '17 at 21:23
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    An iPhone with a properly functioning charger and power management will not overcharge. You are assuming that these phones were not defective. – BobTheAverage Jun 26 '17 at 21:51
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    @BobTheAverage: A defective phone is just as dangerous at daytime than at night. (Possibly *more* dangerous at daytime, as you are more likely to carry it on your person.) A phone is more likely to *become* defective at daytime (when it's being handled). There is no specific danger involved in nighttime charging, except that you are more likely to be asleep. Personally, I think you are *more* likely to be alerted by a fire on your nightstand during the (quiet) night than the (noisy) daytime... – DevSolar Jun 27 '17 at 08:26
  • @BobTheAverage - Yes, I am assuming that, since, by your logic, nothing is safe, ever, because there will the possibility of defect. I see nothing in OP's question to suggest it is asking about anything but normal operation. – PoloHoleSet Jun 27 '17 at 13:28
  • @dev if your phone catches fire during the day, there is a chance you will be able to minimize the damage, if only by calling yourself an ambulance. If your phone catches fire at night, you'll burn to death. – John Dvorak Jul 01 '17 at 14:43
  • @JanDvorak: During the day, a battery fire in my pocket would leave me severely injured, both my thigh and my hand that tried to get the phone out of my pocket. At night, a fire starting a meter away on my bedstand wozld wake me up quickly, and could be easily contained. -- That's the other take, and one is as likely as the other. There is no *systematic* danger of nighttime charging. – DevSolar Jul 01 '17 at 15:48
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Charging you phone overnight is safe, as long as you are sensible. It should be on a hard surface and have adequate room for any heat to vent.

All rechargeable batteries have a risk of causing injury if they are misused or they are faulty. https://en.wikipedia.org/wiki/UPS_Airlines_Flight_6 and there was a problem with the Boeing Dreamliner https://en.wikipedia.org/wiki/Boeing_787_Dreamliner_battery_problems.

Code Gorilla
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