You think airplane mode makes an electronic device safe? Airlines fear devices are even dangerous when off, because lithium-ion batteries may catch fire.

Berlin - The advantages of lithium-ion batteries are evident, but airlines are getting jittery about them, slapping limits on their use aloft.

These rechargeable batteries are everywhere, powering smartphones, notebooks, tablets and other consumer electronics, as well as medical devices.

But they have their drawbacks as well. A ruptured cell can lead to thermal runaway, with temperatures reaching 800 degrees Celsius and explosion.

Samsung's ongoing woes with the Galaxy Note 7 bear eloquent testimony to the problem.

The company recalled 2.5 million of its most modern devices in September, only to hear that one of the follow-up replacements had also gone up in smoke on a US flight in early October.

Precisely that event highlighted airline concerns.

Many have responded by placing a limit on the number of lithium-ion batteries that any one traveller may carry.

Some of the regulations are complex, limiting the output to say 160 watt hours' wattage and compelling passengers to protect spare batteries from short circuit and carry them in their hand luggage.

There are also restrictions limiting the amount of lithium in any one device to 2 grams for example.

And to add to the difficulties, different airlines have different rules, and many require passengers to make special application before boarding with multiple devices or outsize batteries.