The Quiet Killer of Smartphone Batteries: The Habit of Draining to 0%, Latest Research Warns

Persisting until your smartphone's battery is down to 1%, only to start looking for a charger when the screen goes dark. Using your laptop until it completely shuts down, then plugging it in to restart. Draining your EV's range to the last mile before charging.

For many, this isn't an uncommon behavior. Some might even recall the old belief that it's better to fully discharge batteries before charging, a remnant from the days of older rechargeable batteries. However, with the now-dominant lithium-ion batteries, this habit could potentially shorten their lifespan.

Previously, the common culprits for battery degradation were high temperatures, rapid charging, leaving the battery fully charged, and high charging voltages. Indeed, batteries are sensitive to heat. Leaving them at 100% for extended periods can also be taxing. The heat and chemical stress from rapid charging are not negligible either.

However, new insights from a Korean research team have shed light on another overlooked factor. Not only "overcharging" but also "over-discharging" could be quietly causing internal damage to batteries.

The Issue Isn't "0%" Itself, But Deep Discharge

The focus this time is on the cathode material known as NMC in lithium-ion batteries. NMC stands for nickel, manganese, and cobalt layered oxide materials, widely used in electric vehicles. Materials like NMC811, with a high nickel ratio, can enhance energy density but also face challenges in degradation and stability.

The research team examined practical cathode materials like NMC622 and NMC811, investigating how varying the discharge cut-off voltage affected degradation. The discharge cut-off voltage is essentially the lower voltage limit set to prevent further battery use.

Traditionally, using a battery down to a lower voltage seems to yield more energy. Therefore, to maximize range or usage time, one might be tempted to set a lower limit. However, experiments showed that the lower the cut-off voltage, the more severe the degradation. Despite the minimal additional capacity gained in low-voltage regions, the negative impact on lifespan was significant.

In essence, squeezing out the last few percent could be causing significant damage to the battery's internal structure.

"Surface Collapse" Inside the Battery

In lithium-ion batteries, lithium ions move between the cathode and anode during charging and discharging. In a nearly new state, this movement is relatively smooth. However, over time, the electrode surfaces and interfaces degrade, clogging the pathways for lithium ions, reducing capacity, and increasing resistance.

Previously, degradation in NMC cathodes was mainly attributed to oxygen release and structural collapse at high voltages. Excessive lithium extraction during charging destabilizes the material, leading to oxygen loss and a transformation from the original layered structure to a disordered rock-salt-like structure. This is akin to a neatly stacked brick wall collapsing into a pile of rubble.

The significant point of this research is that such structural changes can occur not only during charging but also during discharging. Particularly in deep discharge regions below 3.0V, oxygen is extracted from the cathode surface, leading to lithium oxide and oxygen vacancies. This promotes the transformation from a layered to a rock-salt structure, hindering lithium ion movement.

The research team describes this phenomenon as a "pseudo-conversion reaction." While it doesn't cause as widespread material destruction as a typical conversion reaction, degradation progresses locally but surely on the cathode surface. The challenge is that even if it seems to occur in only a small surface area of the entire battery, it clearly manifests as capacity loss and increased resistance over the long term.

Deep Discharge Also Increases Gas Generation

Degradation doesn't end with structural changes. When oxygen is lost from the cathode surface, side reactions with the electrolyte become more likely. The research confirmed a significant increase in gas byproducts in deeply discharged cells. The original article mentions a substantial increase in gas generation in deeply discharged cells.

Gas generation leads to battery swelling and increased internal resistance. Smartphone batteries bulging, laptop cases lifting, and reduced cell health in EVs and storage batteries are not merely due to aging but involve complex chemical reactions.

This issue is particularly pronounced in high-nickel cathode materials. While increasing nickel content can enhance energy density, it can be detrimental to structural stability. The research showed that high-nickel cells repeatedly subjected to deep discharge rapidly lost capacity, whereas cells with a higher discharge cut-off maintained capacity significantly better.

The key takeaway is that extending battery life doesn't necessarily require new materials or expensive manufacturing techniques. Simply adjusting the discharge cut-off, i.e., revisiting battery management software settings, could help mitigate degradation.

Measures Manufacturers and Users Can Take

The simplest measure suggested by this research is to raise the discharge cut-off voltage. Prevent the battery from being used until it's nearly empty, stopping before it enters dangerous territory. In smartphones, even if it shows 0%, there's often a protective buffer remaining internally. In EVs, the displayed range and charge percentage often have a manufacturer-set buffer behind them.

However, the extent of this buffer varies by design philosophy. Products aiming to showcase longer range or usage time may want to offer more usable capacity. On the other hand, if longevity is prioritized, there needs to be more allowance to avoid chemically harsh regions.

This presents a difficult trade-off for manufacturers. Users prioritize "how much can be used on a single charge." Catalog range and continuous usage time directly influence purchase decisions. However, considering long-term satisfaction, the value of a healthy battery years later is significant.

For users, practical measures are simpler. For smartphones and laptops, charge when the remaining battery is around 20-30%. Avoid the habit of using it down to 0%. Also, avoid long periods in high temperatures or leaving it at 100%. For EVs, avoid unnecessary full charges or deep discharges in daily use, and utilize vehicle-side charge limit settings.

Of course, using it down to near 0% in emergencies doesn't immediately damage the battery. The issue is the repeated deep discharges as a daily habit. Battery degradation progresses not from a single failure but from the accumulation of small burdens.

Not All Lithium-Ion Batteries Are Affected

It's important to note that these findings don't apply equally to all lithium-ion batteries. The research focused on layered oxide cathode materials of the NMC type, particularly those with high nickel ratios.

Recently, the adoption of LFP, or lithium iron phosphate batteries, in EVs has been rapidly expanding. While LFP has disadvantages in energy density compared to NMC, it offers benefits in cost, safety, lifespan, and resources. According to the International Energy Agency, LFP batteries are expected to account for over half of the global EV battery capacity by 2025.

Thus, it's not accurate to assume that "the same degradation occurs to the same extent in all smartphones and EVs." Smartphone batteries have various designs, and EV behavior varies by model, manufacturer, battery chemistry, and battery management system.

Nevertheless, the idea that "draining to 0% is gentle on batteries" is hard to apply to modern lithium-ion batteries. At the very least, avoiding deep discharge is a low-risk longevity strategy for many users.

Reader and Social Media Reactions: "Agreement" and "Criticism"

The comments section of the original article includes reader reactions to this research, reflecting how general users understand battery degradation.

The first reaction is the observation, "Isn't the problem with high voltage more about the current or wattage and the resulting heat from rapid charging?" This is a common question many have. Smartphone chargers are labeled with 5V, 9V, 20V, and rapid charging emphasizes wattage. To users, it naturally feels like "voltage," "current," and "heat" are being discussed interchangeably.

In reality, when discussing battery degradation, it's necessary to distinguish between the voltage supplied by the charger and the electrode potential inside the cell. This distinction can be unclear to general readers. Therefore, scientific articles should not just mention "high voltage" but also clearly explain which part of the voltage they refer to.

The second reaction is, "Isn't it ultimately a problem of heat generated by high-voltage charging?" This is also an important perspective. Heat plays a significant role in battery degradation. However, what makes this research interesting is its focus on chemical changes occurring on the cathode surface at the end of discharge, which cannot be fully explained by heat or rapid charging alone.

The third reaction is a skeptical view: "This has been known for ages." Indeed, among smartphone and laptop users, the rule of thumb to avoid using down to 0% and to operate within 20-80% has been widely known. For those familiar with battery management, the conclusion might not seem novel.

However, the value of this research lies not in the lifestyle advice of "don't use down to 0%" itself, but in demonstrating the material-level mechanisms behind it. When scientific backing is provided for these rules of thumb, manufacturers can more rationally redesign battery management systems. The significance extends from mere trivia for users to guidelines for industrial design.

The fourth reaction is a personal account from a long-time smartphone user. One reader mentions that their Samsung device from 2016 is still operational and has rarely been fully discharged. Of course, a single anecdote doesn't provide scientific conclusions. However, the realization that avoiding deep discharge might be advantageous for long-term use is relatable for many users.

If this topic spreads on social media, reactions will likely split into three main categories: those who agree, saying, "I knew it was better not to use down to 0%," those who see it as merely confirming what was already known, and those who cautiously consider the differences between models and battery types.

Each reaction has its merits. The important thing is not to oversimplify the conclusion into a one-liner life hack. There's no need to fear "0% is absolutely bad." However, the habit of "always charging after it's empty" should be reconsidered for modern lithium-ion batteries.

Battery Lifespan Is Determined by "Design Margin," Not "Endurance"

We tend to think of batteries like fuel tanks: fill them up, use them until empty, then refill. However, lithium-ion batteries are not mere containers. Internally, ions move, side reactions occur on electrode surfaces, and their state gradually changes with temperature, voltage, and usage history.

In this sense, the key to prolonging battery life is not "using it all up," but "avoiding harsh conditions." Don't leave it at 100% in hot places. Avoid frequently dropping it to near 0%. Use rapid charging only when necessary. These small habits can make a difference in battery performance years later.

This research shows that the answer to extending battery life doesn't necessarily lie in dream materials or next-generation batteries. Even with existing lithium-ion batteries, reviewing control over how much to use and where to stop can potentially extend their lifespan.

For smartphones, charge when the battery is at 20-30%. For EVs, avoid excessive full charges or deep discharges in daily use. Manufacturers should focus not only on visible capacity and range but also on buffer design to reduce long-term degradation.

Using the battery to the last drop might seem beneficial in the short term. However, that small gain could turn into a significant loss in the long run.

The simplest step to extend battery life is to start looking for a charger a bit earlier. Instead of panicking when it hits 0%, connect it while there's still some buffer. That small margin can make a big difference inside the battery.

Source URL

ZME Science. An explanatory article on deep discharge degradation in NMC-type lithium-ion batteries by a Korean research team.
https://www.zmescience.com/future/battery-killer-how-to-protect-it-rep/

Paper published in Advanced Energy Materials. A research paper reporting "pseudo-conversion reactions" where oxygen loss and rock-salt structuring occur on NMC cathode surfaces at the end of discharge.
https://advanced.onlinelibrary.wiley.com/doi/10.1002/aenm.202404193

ResearchGate paper page. Used to check the paper's title, authors, abstract, and research content.
https://www.researchgate.net/publication/388068809_Reduction-Induced_Oxygen_Loss_the_Hidden_Surface_Reconstruction_Mechanism_of_Layered_Oxide_Cathodes_in_Lithium-Ion_Batteries

IEA's "Global EV Outlook 2026" explanation on EV batteries. Used to verify supplementary information that LFP batteries accounted for over 55% of the world's EV battery capacity in 2025.
https://www.iea.org/reports/global-ev-outlook-2026/electric-vehicle-batteries