A team of scientists from the University of Warsaw and the Warsaw University of Technology has provided fresh evidence explaining why charging your smartphone to full capacity accelerates battery wear. Using advanced imaging techniques, the researchers observed physical damage forming inside lithium-ion battery materials during deep charging cycles, according to Spider’s Web – technologie.
The study, published in the scientific journal Small Structures (DOI 10.1002/sstr.70589), examined NMC622, a cathode material containing lithium, nickel, manganese and cobalt commonly used in lithium-ion batteries. The research team used electron microscopes and X-ray analysis to track what happens inside the battery when users push charging beyond moderate levels.
Many modern smartphones now offer settings to limit charging to 80 per cent or delay reaching full charge until just before the user typically unplugs the device. The Polish research provides scientific backing for these features by revealing the mechanical stresses that battery materials undergo during the charging process.
What happens inside the battery
Unlike a simple fuel tank that can be filled to the brim without consequence, a lithium-ion battery is a complex chemical system. When you plug in your phone, lithium ions leave the cathode and migrate towards the anode. During use, the process reverses. This movement stores and releases energy.
In NMC622 material, lithium ions occupy spaces between layers built from metal atoms and oxygen. As lithium leaves the cathode during charging, the distances between these layers change. The more deeply you charge the battery, the more lithium is removed, and the greater the structural changes the material must accommodate.
The Warsaw researchers prepared laboratory cells and stopped them at selected stages of operation. They then disassembled the cells and analysed the electrodes using multiple techniques. Scattered light revealed local structural changes, X-ray radiation provided information about atomic arrangement, and electron microscopes enabled direct observation of damage.
The team discovered that the cathode does not charge uniformly. Different fragments of the material exist in slightly different states and respond to changes in varying ways. During deep charging, crystal layers shifted, rotated and bent. The resulting mechanical stresses, under certain conditions, led to cracking.
Why your battery gets worse over time
The research showed that individual sections of cathode material can experience different levels of stress. After 50 charging cycles at various upper voltage limits, the scientists found clear differences in structural damage. Batteries charged to higher levels showed more extensive cracking and deformation.
This explains why phones gradually lose their ability to hold a charge. A device that once lasted all day may demand charging by mid-afternoon after a year or two of use. While many factors influence battery health – including temperature, chemical composition and the number of charging cycles – the structural damage from repeatedly pushing towards full capacity contributes to accelerated aging.
The study does not suggest that reaching 100 per cent once causes immediate harm. Rather, it demonstrates that keeping the battery at very high charge levels for extended periods, or repeatedly extracting maximum capacity, creates cumulative mechanical stress that can shorten overall lifespan.
Should you limit charging to 80 per cent?
If your smartphone offers a charging limit option, the Polish research suggests it is worth considering. Imagine your phone uses about 60 per cent of its capacity during a typical day. Starting at 100 per cent leaves you with around 40 per cent by evening. Starting at 80 per cent leaves about 20 per cent – still sufficient for most users, but with less stress on the battery material.
Many smartphones now include adaptive or optimised charging features. These systems learn your typical charging patterns and may hold the charge at a lower level overnight, topping up to full only shortly before you usually unplug the device. This reduces the time the battery spends at maximum charge.
Of course, if you face a long journey or expect heavy use, charging to 100 per cent remains perfectly reasonable. The key is avoiding unnecessarily maintaining high charge levels when moderate capacity would suffice for your daily needs.
What this means for Poles in the UK
The findings from Warsaw researchers offer practical guidance for anyone wanting to extend their smartphone’s useful life, which is particularly relevant given the high cost of flagship devices in the UK market. Most iPhones and recent Android phones include battery optimisation settings – check under Battery in your device settings.
For those on tight budgets or planning to keep their phone for several years, adopting an 80 per cent charging limit could postpone the need for an expensive battery replacement or new device. Apple charges between £69 and £105 for out-of-warranty battery replacements, while third-party services typically cost £40 to £80.
If you use your phone heavily for work, navigation or photography, you may need the full capacity. However, for typical daily use – messaging, browsing and moderate app usage – the research suggests that leaving some capacity unused is a sensible trade-off for longer battery health. Enable optimised charging features where available, and avoid leaving your phone plugged in at 100 per cent for many hours overnight if your device does not manage this automatically.
