A battery pack shows visible swelling. What is the appropriate action?

Swelling in a lithium-polymer pack means gas has been generated inside a sealed cell, which happens when the electrolyte breaks down from overcharge, over-discharge, physical damage or heat. That gas is a one-way signal: the chemistry that produced it does not reverse, and the cell will not recover on a later charge cycle. A swollen pack is at elevated risk of thermal runaway, a self-sustaining reaction that cannot be extinguished by removing power and that burns hot enough to ignite whatever it is sitting on. Part 107 does not publish a battery-condition rule by section, but §107.15 requires the remote pilot to determine the aircraft is in a condition for safe operation before every flight, and a swollen pack fails that check outright.

Swelling is evidence of internal cell failure, so the pack comes out of service permanently and goes to proper disposal or recycling. There is no inspection, cycle or cooldown that returns a swollen pack to airworthy condition. Retiring it is the only action consistent with the preflight determination the remote pilot is required to make.

Small unmanned aircraft run on lithium-polymer packs, which store energy densely and fail energetically. Under §107.15 the remote pilot in command must check that the aircraft, including its power system, is in a condition for safe operation before each flight, and must discontinue a flight when it is not.

Puffed Means Finished. A swollen pack is a one-way door — gas out, battery out. No charge cycle, no cold storage and no short hop brings it back.

Battery questions on the UAG reward the conservative answer. If an option keeps damaged hardware flying under any restriction, it is wrong.

• •Treating swelling as a charge-state problem that a discharge cycle can fix
• •Keeping a damaged pack in service under a self-imposed restriction such as short flights
• •Assuming cold storage or cold-weather use halts the failure