That's an interesting question! I've never really thought about how altitude changes might affect electronic devices like power banks. Let me try to wrap my head around this.

First off, I know that air pressure decreases as altitude increases. So, in an airplane, as it ascends, the pressure inside the cabin decreases compared to the pressure at sea level. This is why some people experience discomfort in their ears during takeoff and landing—the pressure differences cause their eardrums to bulge or retract.

Now, applying this to power banks or any airtight electronic device, if it's sealed perfectly, the pressure inside remains constant while the outside pressure decreases. This should cause the device to expand slightly due to the pressure difference, just like how a balloon expands as it rises.

But how significant is this expansion? I mean, power banks are small and probably don't have much air inside them. Maybe there's some air in the battery compartment or around the internal components, but it's likely minimal. So, the expansion might not be noticeable.

However, if there's any gas inside the device, like hydrogen or helium, which are sometimes used in batteries or other components, that could expand more than air, leading to greater pressure differences.

But even with that, I don't think the expansion would be significant enough to cause any structural issues or safety hazards on an airplane. Modern electronic devices are designed to withstand some amount of pressure variation.

Moreover, airtight devices are usually built to handle pressure changes without leaking or bursting. So, a well-designed power bank should be fine.

Another thing to consider is that airplanes have pressurized cabins to maintain a comfortable environment for passengers. The cabin pressure is typically kept at a level equivalent to the air pressure at around 8,000 feet above sea level. So, the pressure difference between the cabin and the outside is less severe than if the cabin was unpressurized.

Therefore, the pressure changes experienced by electronic devices inside the cabin are not as extreme as those outside the plane.

Also, it's worth noting that many electronic devices, including power banks, have vents or small openings to allow for pressure equalization. These vents are designed to prevent pressure buildup inside the device, which could cause damage or affect performance.

So, even if there's some pressure change, the venting system should help alleviate any potential issues.

Moreover, power banks contain batteries, which are sensitive to temperature changes. But pressure changes are different, and batteries are generally less affected by pressure variations compared to temperature.

There have been instances where electronic devices have caused aviation safety issues, but those are usually due to overheating or short circuits, not pressure changes.

In conclusion, while altitude changes can cause some expansion in airtight devices due to pressure differences, it's unlikely that this would lead to significant safety issues with power banks on airplanes. Modern devices are designed to withstand such variations, and the cabin environment is controlled to minimize these effects.

I hope this helps! If you have any more questions, feel free to ask.