Originally Posted by winkydink
If it's a lead-acid battery, I could see them having some issue. Think about it.
As long as a UPS battery is compliant with IATA/ICAO special provision A67, it is classified as non-dangerous even though it may be a lead-acid cell.
My understanding is that the overwhelming majority of modern UPS cells are compliant (i.e. non-spillable even in case of a cracked/ruptured case). If in doubt, it should be simple enough to discover from the manufacturer.