4 Everyday Charging Mistakes to Avoid for Better Smartphone Battery Health

Lithium-ion batteries do not experience failure simply due to aging or the passage of time. Rather, they tend to fail as a consequence of the numerous events that transpire within them thousands of times each day, specifically during each individual charge cycle. Gaining a clear understanding of the intricate processes occurring inside the cell transforms these formerly held beliefs from mere superstition into a foundation of logical reasoning.

Keep the Charge Between 20% and 80%

Lithium-ion cells store energy by moving lithium ions between two electrodes, a graphite anode and a metal-oxide cathode, through a liquid electrolyte. At very high charge states, the cathode lattice is under mechanical stress because so many ions have left it. At very low charge states, the anode is under stress from the opposite condition. Both extremes accelerate a process called electrode degradation, where the crystal structure of the electrode material slowly breaks down and can no longer hold ions in place. Keeping the battery in the middle range, roughly 20% to 80%, keeps both electrodes in a lower-stress state for most of their working life. The top and bottom 20% are where the chemistry is least stable.

Avoid Leaving the Phone on Charge All Night

Modern phones stop drawing current once the battery reaches 100%, so overnight charging does not overcharge in the old sense. The problem is trickle charging. Once the battery discharges slightly from standby use, the charger tops it back up to 100%. This keeps the cathode in its highest-stress state for hours at a time, night after night. Some phones now offer a setting that holds the charge at around 80% until shortly before a typical wake time, then finishes the charge. That setting exists precisely to reduce the hours spent at peak voltage. If yours has it, turn it on. If not, plugging in an hour before you sleep and unplugging when you wake achieves much the same thing.

Charge at a Moderate Rate When You Have the Choice

Fast charging works by pushing more current into the cell in less time. The problem is heat. Higher current means more resistance heating inside the cell, and heat accelerates a side reaction called electrolyte decomposition. The electrolyte, the liquid that lets ions travel between electrodes, breaks down gradually under heat, forming a resistive layer on the anode called the solid electrolyte interphase. A thicker SEI layer means the battery holds less charge and charges more slowly over time. Slow or standard charging generates far less heat, so the SEI grows more slowly. Fast charging when you are in a hurry is a reasonable trade-off. Using the fastest charger available every single time is not.

Do Not Let the Phone Get Hot While Charging

Heat is the single biggest accelerant of every chemical degradation process in a lithium-ion cell. At elevated temperatures, electrolyte decomposition speeds up, lithium plating on the anode becomes more likely, and the separator, the thin membrane between the two electrodes, degrades faster. Lithium plating is worth understanding: at high temperatures and high charge rates, lithium ions can deposit as metallic lithium on the anode surface rather than intercalating into the graphite. These deposits, called dendrites, can eventually pierce the separator, which is a serious safety risk as well as a capacity killer. Practical consequence: do not charge under a pillow or inside a case that traps heat. If the phone is warm from use, let it cool before plugging in. A phone that is hot to the touch while charging is doing measurable damage to its own cells.