Why flagship phones cap battery sizes: shipping limits, dual cells, and silicon‑carbon

Against a wave of Chinese smartphones boasting 7,000–8,000 mAh batteries, the packs inside iPhone, Galaxy, and Pixel look modest. Even the Galaxy S25 Ultra tops out at 5,000 mAh, and the iPhone 17 Pro Max only nudges past that mark. On paper it seems puzzling; in practice, there’s a clear logic to it.

Part of the story is design and thickness. Premium devices chase ultra‑thin bodies — the iPhone Air measures just 5.6 mm, which physically limits battery size. Yet there’s a counterexample: the Chinese RedMagic 11 Pro fits 7,500 mAh into an 8 mm frame and even supports wireless charging. Slim doesn’t always have to mean small capacity, but the trade‑off is real.

The bigger reason, though, sits outside design and inside international shipping rules. Regulations classify lithium‑ion batteries above 20 Wh — roughly 5,400 mAh — as Class 9 dangerous goods. That triggers higher transport costs, special packaging, and extra permits. Unsurprisingly, Apple, Samsung, and Google try to stay below that threshold. The ceiling here is set less by ambition than by logistics.

Chinese brands have found a workaround: two smaller batteries instead of one large cell. Each unit stays under the 20 Wh limit, but together they add up to 7,000 mAh or more without breaking shipping rules. In parallel, companies like OnePlus, Honor, Xiaomi, and RedMagic are pushing silicon‑carbon batteries with higher energy density, moving the needle on endurance in a way that feels rapid and deliberate.

Silicon can hold up to ten times more charge than lithium, but it can expand by as much as 300% during charging, risking cell damage. Manufacturers counter that with nanostructures and chemical coatings. Even so, the shift demands new production lines, certifications, and pricey materials — a costly transition for Apple, Samsung, and Google, which have already poured billions into conventional lithium‑ion.

Silicon‑carbon cells also call for new power‑management systems, different degradation profiles, and reworked charging chips. That raises the odds of mistakes — and after the Galaxy Note 7 incidents, Samsung stays especially careful. Apple, for its part, tends to introduce radical changes only after extended internal testing. The caution may feel conservative, but it’s consistent with their risk calculus.

Progress, however, looks inevitable. Forecasts point to Samsung, Apple, and Google beginning a gradual switch to silicon‑carbon batteries between 2027 and 2030. Early gains should be modest — a 5–10% bump in capacity — translating to around 5,500 mAh in future Galaxy Ultra models and roughly 6,000 mAh for the iPhone Pro Max lineup.

Until then, Chinese phones are likely to lead on battery life, rapidly advancing silicon‑carbon tech. They may well be the first to ship smartphones with 10,000 mAh packs — even if the logo on the case isn’t Apple or Samsung.