Welcome! In this article, we will break everything down in a simple and practical way.
Introduction
Many of us still remember the infamous Samsung Galaxy Note 7 incident, which highlighted just how volatile phone batteries can be when they fail. In that case, faulty batteries could overheat, enter thermal runaway, and in some instances catch fire. Since then, manufacturers have put a lot of effort into making modern batteries safer, and serious failures like that have become extremely rare. That said, lithium-ion batteries don’t last forever, and they naturally degrade over time, becoming less stable as they age. This brings me to my mom’s phone, which was nearly six years old when its battery ultimately failed and caught fire one morning. Granted, this is not something most people will ever experience, but there were warning signs beforehand that are worth knowing about—especially if you’re using an older phone.
The battery can’t last very long
A dramatic drop in battery life is one of the first signs of a failing battery
Batteries lose capacity as they age, typically by around 10% per year, depending on usage patterns and how well you take care of battery health. This alone is nothing to worry about—it’s completely normal for any phone (or lithium-ion battery, for that matter), and it’s inevitable that your phone’s maximum battery capacity will decline over time. That said, reduced capacity is still one of the most obvious symptoms of the chemical and structural changes taking place inside the cell. One of the more important changes is dendrite formation—tiny needle-like lithium structures that can develop as a battery ages. If a battery remains in service far beyond its intended lifespan, these dendrites can eventually grow large enough to pierce the internal separator that keeps the positive and negative sides apart. When that happens, it can cause an internal short circuit, potentially resulting in a dead battery or, in rare cases, thermal runaway and fire. One of the easiest ways to reduce the risk is to replace the battery once it falls to around 75–80% of its original capacity. As a bonus, you’ll also get a more enjoyable experience with the phone.
Brand
YEREADW
Cable Type
Type-C
This inexpensive USB-C power meter lets you see how much voltage, current, and power your phone is drawing while charging. It can also help identify charging issues and estimate battery capacity by measuring how much energy the battery accepts during a full charge cycle.
The back of the phone feels unusually warm during normal use
Persistent heat can point to a deeper problem
Credit: Justin Duino / How-To Geek
It’s completely normal for a phone to get warm (or even slightly hot) during regular use, particularly during charging or heavy tasks like gaming. A warm phone doesn’t automatically sound the alarm, and some phones are designed to run warmer than others. If you’ve had your phone for a while, you’ve likely grown accustomed to how it feels in the hand and how warm it gets, especially during lighter tasks like scrolling Facebook or editing documents. However, if an older phone suddenly starts feeling noticeably warmer than it used to during those same activities, it’s worth paying attention. Aging batteries become less efficient over time as their internal resistance increases, and that extra inefficiency often shows up as excess heat. In fact, the phone getting too hot to hold comfortably can indicate the start of a thermal runaway. It was the very last warning sign before my mom’s phone caught fire. Again, I have to reiterate that this is a rare outcome, but if your phone ever feels alarmingly hot for no obvious reason, it’s a good idea to stop using it temporarily, unplugging it, and maybe even placing it in a fireproof container.
Quiz8 Questions · Test Your KnowledgeAccidentally dangerous gadgetsTrivia challengeSome tech was built to help — but ended up causing chaos, injuries, and even fires.SafetyHistoryRecallsDesignHazardsBeginSamsung recalled millions of Galaxy Note 7 smartphones in 2016 primarily because of what dangerous defect?AScreens cracking under normal pressureBBatteries overheating and catching fireCSoftware causing random emergency callsDCharging ports delivering electric shocksCorrect! The Galaxy Note 7’s lithium-ion batteries had a manufacturing flaw that caused them to short-circuit and combust. The situation was so serious that the phones were banned from commercial flights worldwide, and Samsung ultimately discontinued the entire product line.Not quite. The Galaxy Note 7 was recalled because its batteries would overheat and catch fire — sometimes violently. The crisis was so severe that airlines banned the device from all flights and Samsung killed the Note 7 entirely.ContinueHoverboards became notorious in 2015 and 2016 for frequently doing what dangerous thing?ACausing falls due to sudden speed surgesBEmitting toxic fumes during chargingCCatching fire due to cheap lithium-ion battery packsDInterfering with Wi-Fi and medical devicesThat’s right! Early hoverboards used low-quality, unregulated lithium-ion battery packs that were prone to thermal runaway — meaning they could burst into flames while riding or charging. Hundreds of house fires were linked to the devices before safety standards were enforced.Not quite. The big hoverboard danger was fire. Cheap, unregulated battery packs caused thermal runaway events, sparking hundreds of house fires across the US and UK and triggering a wave of import bans and safety investigations.ContinueThe Therac-25 radiation therapy machine in the 1980s became a cautionary tale in engineering because it caused patient deaths due to what?AA hardware short circuit that doubled radiation outputBSoftware bugs that delivered massive radiation overdosesCFaulty shielding that leaked radiation into hospital corridorsDA design flaw in the targeting lens that misfocused the beamExactly right! The Therac-25’s software had race conditions — timing bugs that could occur when operators typed commands quickly. In certain cases this removed safety interlocks and delivered doses up to 100 times the intended amount, killing at least three patients. It remains one of the most studied disasters in software engineering history.The culprit was actually software bugs — specifically race conditions that disabled hardware safety checks under certain operator inputs. The result was lethal radiation overdoses. The Therac-25 is now a foundational case study in why software safety cannot replace physical hardware interlocks.ContinueEarly versions of which popular fitness gadget were recalled after the device’s wristband caused skin burns and rashes in thousands of users?AApple Watch Series 1BGarmin Forerunner 235CFitbit ForceDJawbone UP24Correct! Fitbit recalled its Force wristband in 2014 after thousands of users reported contact dermatitis, skin irritation, and even burns. The issues were linked to allergic reactions to the nickel in the stainless steel casing and adhesives in the band material. It was a costly recall that led Fitbit to redesign future bands.It was actually the Fitbit Force that was recalled in 2014 after causing widespread skin irritation and burns. The culprit was a combination of nickel in the hardware and adhesives in the band material that triggered serious allergic reactions in many wearers.ContinueThe original Microsoft Surface Pro power connector was quietly redesigned after reports that the charging cable could do what?AFray and expose live wires, posing a fire and shock riskBAccidentally trigger BitLocker lockouts on connected devicesCOverheat the battery if left plugged in overnightDDamage USB ports on third-party hubs when connected simultaneouslyRight on! The Surface Pro’s proprietary charging cables were widely reported to fray near the connector end, exposing live electrical wires. Microsoft faced significant user complaints and a class-action lawsuit over the issue. The problem highlighted how cable strain relief design is a critical — and often overlooked — safety factor.The real issue was cable fraying. The Surface Pro charging cables were prone to splitting open near the connector, leaving bare live wires exposed. This created both fire and electrocution hazards, and Microsoft faced lawsuits and significant criticism over the design.ContinueLawn darts, sold as a family garden game in the 1970s and 1980s, were eventually banned in the US and Canada. What made them so dangerous?AThe plastic flights would shatter into sharp fragments on impactBThey had heavy metal-tipped points designed to spike into the groundCThe darts contained trace amounts of toxic lead-based paintDTheir aerodynamic design made them travel unpredictably farSpot on! Lawn darts — also known as Jarts — featured heavy steel-tipped spikes meant to stick into the ground. When thrown into the air and landing on a person, they acted essentially like a javelin. The US Consumer Product Safety Commission banned them in 1988 after they were linked to thousands of injuries and multiple deaths, many involving children.The danger was their sharp, heavy metal tips. Lawn darts were essentially javelins sold as toys — when they came down on a person instead of the grass, the results were catastrophic. The CPSC banned them in the US in 1988 following multiple deaths, predominantly among children.ContinueWhich early consumer technology product was found to expose users to low levels of X-ray radiation due to a manufacturing defect in its vacuum tubes?AEarly cathode ray tube televisions in the late 1960sBFirst-generation microwave ovensCReel-to-reel tape recordersDTransistor radios with faulty tuning componentsCorrect! In 1967, General Electric recalled around 90,000 color televisions after it was discovered that faulty high-voltage regulators in the CRT sets were emitting X-ray radiation at levels exceeding federal safety guidelines. The incident prompted the US government to pass the Radiation Control for Health and Safety Act in 1968.The answer is early color televisions. In 1967, GE had to recall tens of thousands of color TV sets because defective components in their cathode ray tubes were leaking X-ray radiation. The scandal was serious enough to prompt the US Congress to pass new radiation safety legislation the very next year.ContinueTakata airbag inflators, subject to the largest automotive recall in history, were dangerous because their inflators could do what upon deployment?ADeploy at half pressure, failing to protect occupants in crashesBRupture and send metal shrapnel into the vehicle cabinCRelease toxic nitrogen dioxide gas into the passenger compartmentDTrigger spontaneously without a collision due to sensor errorsExactly right! Takata used ammonium nitrate as the propellant in their inflators without a chemical stabilizer. Over time — especially in hot, humid climates — the compound degraded and could explode with excessive force, shattering the metal inflator housing and firing shrapnel directly at passengers. The defect was linked to over 27 deaths and hundreds of injuries worldwide.The terrifying truth is that Takata’s inflators could literally explode, turning the airbag housing into a metal fragmentation device firing shards into the car’s occupants. A degraded ammonium nitrate propellant was the chemical culprit, and the defect caused more than 27 deaths globally in the largest auto recall ever recorded.See My ScoreChallenge CompleteYour Score/ 8Thanks for playing!Try Again
The battery percentage jumps around or gets stuck
An unreliable charge indicator sometimes signals a failing battery
Credit: Justin Duino / How-To Geek
Another warning sign of an aging battery you should be on the lookout for is an erratic battery percentage. You’ve probably experienced this at some point with a battery-powered device (maybe a laptop), when the battery is sitting at 68% for an hour, and then suddenly drops to 15% within minutes. This is because your phone doesn’t actually know the exact charge in your battery—it’s merely taking an educated guess based on a few factors, mainly voltage. In an aging battery, voltage can appear to be stable at a certain percentage, but when the phone draws a sudden burst of current, the voltage plunges rapidly (this is called voltage sag). The phone thinks the battery is almost empty, which is why the battery percentage drops. As the load decreases, the voltage slowly rebounds, and the percentage might even go up by a few points. Phones have gotten a lot better at estimating charge, and you can sometimes improve accuracy by recalibrating the battery: draining the phone until it dies completely, then charging it to 100%. But in any case, this is a sign that your battery has degraded significantly, to the point that its voltage is fluctuating rapidly.
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The phone reboots randomly or shuts down with charge remaining
Unstable power can lead to a lot of problems
Credit: Justin Duino / How-To Geek
Much like with a fluctuating battery percentage, another warning sign that the battery’s voltage isn’t stable is the phone randomly rebooting or shutting down, even though you’ve charged it only a few hours ago and know for a fact that the battery isn’t empty. This happened to my mom’s phone sometimes, and it started about a year before it caught on fire. This most often happens when the load suddenly increases, like when you open an app or boot up a game. The phone thinks the battery is about to lose its charge completely, so it shuts down to prevent the battery from being drained too far, as lithium-ion batteries can become unusable if they drop below a critical voltage threshold.
The back of the phone is separating from the frame
A swollen battery can push a phone apart from the inside
Credit: Ismar Hrnjicevic / How-To Geek
Lithium-ion batteries swell as they age. This is inevitable, as the liquid electrolyte slowly breaks down and releases volatile gases like carbon dioxide, methane, and hydrogen. The battery is actually allowed to swell by design, and manufacturers achieve this by using flexible pouches that act as a balloon—and this appearance is how these dangerous batteries earned their nickname “spicy pillows.”
The danger with these swollen batteries comes from multiple angles. First, as the battery expands, the separator layer gets stretched thin, effectively acting like a vice grip. This makes it much easier for those spiky dendrites I mentioned earlier to poke through the separator layer, cause a short circuit, and heat up rapidly. Some aging phones with these spicy pillows create so much pressure from the inside that they take the phone apart, pushing the back and display away from the frame. That’s what happened to my old Realme, but it didn’t happen to my mom’s Realme. So, if you notice any kind of physical separation like this, it’s a major warning sign that your battery needs to be replaced. However, since some phones use stronger glue, it doesn’t actually have to manifest on the outside for the battery to swell on the inside.
Your phone likely won’t self-ignite, but an aging battery still deserves attention
Despite the headlines that occasionally make the news (including this one), smartphone battery fires are remarkably rare. Millions of aging phones continue to remain in service without experiencing any major battery-related issues, especially models from major manufacturers that undergo extensive development, research, and testing. My goal here isn’t to make you worry about your phone suddenly catching on fire. Rather, it’s to help you recognize the warning signs early and incentivize you to replace the battery after a few years of use, especially if you’re still happy with the device. The best part? You’ll be awarded with longer battery life, performance, and reliability!
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Conclusion
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