Airline check-in luggage rules are such nonsense. Li-ion batteries are not allowed (short-circuit risk?), but devices containing Li-ion batteries are, but then mobile "batteries" aren't (but they're a power supply device, not a battery?), but a combo BT speaker+battery is OK.
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No airline I've flown with allows laptops with batteries attached in the hold. Can put them in the hold with the battery in your carry-on, but that's it. Also I wouldn't ever leave a laptop in my checked in luggage, for so many other reasons.
I've checked in laptops with attached batteries multiple times in the past year. Yes, there are reasons not to, but sometimes when you carry 3 laptops with you it's nice not having a >15kg backpack.
