Use voltage × Ah when both values are available, or use the battery’s marked Wh rating. The cited FAA page does not supply an mAh conversion, and its wording for larger batteries is ambiguous; check authoritative details and airline limits before relying on a size allowance.
First check whether it is a spare battery
The FAA guidance covers spare, uninstalled lithium-ion batteries, including power banks. Batteries installed in devices such as laptops and phones are directed to separate guidance, so identify which case applies before using the spare-battery limits.
Use the FAA formula when the label gives Ah
The FAA says to calculate watt-hours by multiplying battery voltage by amp-hours (Ah). If both values appear on the label, multiply them to get Wh, then compare that result with the FAA’s stated size limits. The FAA also notes that newer lithium-ion batteries often have the Wh rating marked directly.
A mAh label needs another supported step
The cited FAA page does not give a method for converting milliamp-hours (mAh) to amp-hours. So if a label gives mAh but not Wh or Ah, this source alone does not complete the calculation. Do not treat the mAh number as if it were Wh; use a clearly marked Wh rating or obtain the missing conversion information from an authoritative source before relying on a size comparison.
Read the larger-battery wording carefully
The FAA lists a 100 Wh limit per spare rechargeable lithium-ion battery, then describes an allowance for up to two larger batteries with airline approval using the phrase “exceeding 101–160 Wh.” That wording does not state a clear lower boundary. The source supports preserving the stated approval and two-battery conditions, but it does not resolve that boundary, so do not infer a precise qualifying range from this page alone.
Check carrier limits too
The FAA says many airlines may impose stricter quantity and Wh limits for power banks, regardless of capacity. Its guidance therefore does not settle every carrier’s conditions. Check the airline’s restrictions as well as the FAA page before travel.
Sources & scope
An AI-assisted explainer checked against the linked primary sources. Source review dates are not necessarily announcement dates.