Where do spare batteries and power banks go when you fly?

In the carry-on, always, and never in a checked bag. That rule is about loose cells and power banks — the trimmer with its battery inside may travel in either.

This is the half of the lithium rule that is genuinely restrictive, and it is the half people apply to the wrong object. The TSA and the FAA allow a device with its battery installed in checked baggage; a spare lithium cell or a power bank has to be in the cabin with you.

Why the hold is the problem. A lithium cell that fails does so quickly and hot, and a fire in the hold is out of reach: nobody can see it start and nobody can put it out. In the cabin, a bag that begins to smoke is dealt with in seconds. That is the whole of the reasoning, and it is why the rule is about accessibility rather than about the battery being dangerous in itself.

What counts as a spare. A loose rechargeable cell, a power bank, a charging case with its own battery. A grooming tool with a sealed internal cell does not count, which is the point of can I take a beard trimmer in carry-on baggage.

Two practical conditions. Protect the terminals — the original packaging, a plastic bag or tape over the contacts — because a short against keys or coins is the realistic failure. And watch the capacity: up to 100 watt-hours needs no permission, 101 to 160 Wh needs the airline’s agreement, and above that it does not fly. A power bank states its capacity in mAh and often in Wh; a 10,000 mAh bank at 3.7 V is about 37 Wh, comfortably inside the limit.

Does a grooming tool need a power bank at all? Rarely, and do I need a power bank for travel answers it with the tools on this site: several Philips models ship with a USB-A cable and no wall adapter, so any USB source already charges them.

For a particular flight, the airline’s own published conditions are the authority — they can be stricter than the federal rule, never looser.

Check your own manual before you follow anything here. Temperatures, water ratings and supply voltages differ from model to model, and the maker’s own figures take precedence over anything written on this site. A supply of the wrong voltage is a failure rather than a slow charge, and the figure is printed on the tool — not inferred from a connector that happens to fit.