Chinese phone makers, including Xiaomi, Oppo, and OnePlus, have standardized much larger smartphone batteries but this trend has yet to reach the big names such as Samsung, Apple, and Google, which have avoided significantly increasing battery sizes in their flagship devices.

A new explanation points to US federal transportation regulations as the key reason. The information was shared by tipster Ice Universe on X, who cited US lithium battery transport rules under 49 CFR 173.185.

These regulations limit lithium-ion battery cells to a maximum of 20 watt hours (Wh) for simplified transport and handling. Batteries that exceed this threshold fall into stricter hazardous goods classifications, requiring additional packaging, labeling, and documentation.

20Wh Battery Limit for US

Lithium battery transportation is governed primarily by US Federal Regulation 49 CFR 173.185 and International Air Transport Association dangerous goods rules. Under these guidelines, lithium ion cells with capacities of 20Wh or less do not require special hazardous goods handling.

However, batteries exceeding 20Wh are classified as Class 9 dangerous goods. These require more complex shipping procedures, including special packaging and documentation.

Smartphone batteries are typically treated as single lithium-ion cells, meaning manufacturers design them to stay within the 20Wh limit to simplify logistics and compliance.

The mystery behind why Samsung, Apple, and Google don’t significantly increase battery sizes has been solved, with the primary reason being U.S. federal regulations on lithium battery transportation, 49 CFR 173.185: For lithium-ion battery cells, the limit is 20 Wh.

Overview of… pic.twitter.com/NbdDR7wais

— Ice Universe (@UniverseIce) July 3, 2025

Battery Capacity Calculations

Typical smartphone battery voltage ranges between 3.7V and 3.85V. Using this voltage range, battery capacity in watt-hours can be calculated using the formula:

Wh = (mAh × Voltage) ÷ 1000

For example:

• 4000 mAh at 3.85V equals approximately 15.4Wh
• 5000 mAh at 3.85V equals approximately 19.25Wh
• 5500 mAh at 3.85V equals approximately 21.18Wh, which exceeds the 20Wh limit
• 6000 mAh at 3.85V equals approximately 23.1Wh, which significantly exceeds the limit

This calculation explains why most flagship phones stay around the 4000 mAh to 5000 mAh range.

Major Flagships Remain Within Limit

Battery capacities of major flagship smartphones in the US market show consistent adherence to the 20Wh threshold.

Apple’s iPhone 16, iPhone 16 Pro, and iPhone 16 Pro Max feature batteries ranging from 3355 mAh to 4702 mAh. At approximately 3.8V, these translate to roughly 12.75Wh to 17.87Wh.

Samsung’s Galaxy S25, Galaxy S25 Plus, and Galaxy S25 Ultra include batteries between 4000 mAh and 5000 mAh. These equate to approximately 15.4Wh to 19.4Wh.

Google’s Pixel 9 series includes batteries between 4700 mAh and 5100 mAh. At approximately 3.85V to 3.89V, these translate to about 19.68Wh.

Dual Cell Designs Can Bypass Limits

Some manufacturers use dual-cell battery designs to increase total capacity while keeping individual cells under the 20Wh limit.

For example, the OnePlus 13 includes a 6000 mAh battery, approximately 23.22Wh in total. However, it uses two separate battery cells, ensuring each individual cell remains within the 20Wh threshold.

This approach allows companies to offer larger total battery capacity while complying with transportation regulations.