Chinese smartphone makers like Xiaomi, Oppo, and OnePlus have pushed battery sizes upward in recent years, but major US-market flagships from Samsung, Apple, and Google have largely avoided making significant jumps in battery capacity. A new explanation suggests that US federal transportation rules on lithium-ion batteries are a key reason behind this trend.
Tipster Ice Universe shared on X that US lithium battery transport regulations under 49 CFR 173.185 impose a 20 watt-hour (Wh) limit for simplified shipping and handling. Batteries that exceed this limit are classified as hazardous goods, triggering stricter requirements such as special packaging, labeling, and additional documentation. Since most smartphone batteries are treated as single lithium-ion cells, manufacturers design them to stay under 20Wh to keep logistics and compliance straightforward.
Lithium battery transportation is governed by US Federal Regulation 49 CFR 173.185 as well as International Air Transport Association (IATA) dangerous goods rules. Under these guidelines, lithium-ion cells with capacities of 20Wh or less do not require special hazardous goods handling. However, batteries above 20Wh fall into Class 9 dangerous goods, demanding more complex shipping procedures.
Battery capacity in watt-hours is calculated using the formula Wh = (mAh × Voltage) ÷ 1000. Typical smartphone battery voltage ranges from 3.7V to 3.85V, meaning that:
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4000 mAh at 3.85V is roughly 15.4Wh
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5000 mAh at 3.85V is roughly 19.25Wh
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5500 mAh at 3.85V is roughly 21.18Wh, which exceeds the 20Wh limit
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6000 mAh at 3.85V is roughly 23.1Wh, significantly above the limit
These calculations help explain why flagship phones typically stay in the 4000–5000 mAh range in the US market.
Major flagship models reflect this compliance. Apple’s iPhone 16 series batteries range from 3355 mAh to 4702 mAh, translating to about 12.75Wh to 17.87Wh at approximately 3.8V. Samsung’s Galaxy S25 series uses batteries between 4000 mAh and 5000 mAh, equating to about 15.4Wh to 19.4Wh. Google’s Pixel 9 lineup has batteries from 4700 mAh to 5100 mAh, translating to around 19.68Wh at roughly 3.85V to 3.89V. All of these remain below the 20Wh threshold.
Some manufacturers have found ways to increase total battery capacity while still complying with transport rules by using dual-cell designs. For example, the OnePlus 13 packs a 6000 mAh battery, approximately 23.22Wh total, but uses two separate cells so each remains under the 20Wh limit. This allows larger total capacity without violating shipping regulations, offering a practical workaround for companies looking to deliver longer battery life in their devices.
