Smart rings compress a lithium-ion cell into one of the most constrained form factors in consumer electronics. A battery that would sit as a flat rectangle in a phone has to curve around a finger, fit inside a rigid metal shell, and still deliver days of runtime. Understanding why that is difficult starts with how these cells are actually built.
Why do lithium-ion batteries swell?
A modern battery looks like a solid block, but internally it is an active chemical system that never fully stops reacting. Electrolyte decomposition, side reactions at the electrode surfaces, and elevated temperature all generate gas over the life of a cell. That gas has nowhere to go, so the cell expands.
Swelling is generally a symptom rather than a root cause. It signals that something inside the cell has departed from its intended condition, which is why a swollen battery in any device is treated as a warning rather than a cosmetic problem.
Why is the smart ring form factor so demanding?
Lithium-ion cells do not start as blocks. The electrodes begin as long, thin strips that are wound or folded many times to pack the maximum active area into a given volume. Energy density is largely a function of how many layers fit and how precisely they stack.
Every fold is an opportunity for a defect. Misalignment, uneven pressure, a wrinkle in a separator layer, or contamination introduced during assembly all become permanent features of the finished cell. A ring compounds this by requiring the stack to follow a curve rather than a flat plane, inside a total volume smaller than almost any other consumer battery application.
The enclosure matters too. A rigid outer shell will not deform to accommodate expansion, so any swelling is directed inward toward the wearer rather than outward. Once the device is in service, vibration, temperature cycling, and charge cycling add stress to whatever variation was already present.
What happened with the Galaxy Ring
In September 2025 a user reported that his Galaxy Ring swelled while being worn, could not be removed, and required a hospital visit to take off. The incident circulated widely and raised broader questions about battery safety in wearables.
Samsung investigated for roughly three months with an independent external agency and attributed the swelling to a crack in the internal moulding structure of that specific unit, stating that it found no wider battery safety risk associated with the product.
That outcome is worth noting carefully, because it points at exactly the kind of problem non-destructive inspection exists to catch. A crack in an internal structure is invisible from the outside and cannot be found by any external examination. Finding it conventionally means destroying the device, which means the specific unit that failed can no longer be studied.
What X-ray inspection shows in a cell this small
Computed tomography of an assembled smart ring resolves the internal layer structure without opening the device. The wound electrode stack, the alignment and spacing of its layers, the surrounding moulding and housing structures, and the interfaces between them are all visible in a reconstructed volume.
That makes several failure-relevant conditions detectable. Electrode misalignment and irregular layer spacing show up geometrically. Voids, delamination, and gaps appear as density differences. Foreign material introduced during assembly appears as a density anomaly against the surrounding structure. Cracks in internal moulding and housing components are visible in cross-section.
None of this requires cutting the device open, which matters twice over. In production it means cells can be sampled without scrapping them. In failure analysis it means the evidence survives the investigation.
Why this extends beyond one product
The pressures driving this are industry-wide rather than specific to any manufacturer. Devices keep demanding more energy from less volume, which pushes cell design toward higher energy density and more aggressive packaging at the same time. Airlines have tightened rules around portable power banks. Aging phone batteries swell in storage. Power tool packs have caused workshop fires. The Galaxy Note 7 recall remains the reference case for how expensive a battery problem becomes at scale.
Every one of those outcomes traces back to internal conditions that are invisible from the outside of a finished cell. As form factors get harder to build, the ability to see inside one without destroying it stops being a diagnostic convenience and becomes part of how quality is verified in the first place.
