Sudden decompression of lithium-based batteries
The risk posed by lithium-based batteries is, of course, fire. A fire can be triggered by several mechanisms, one being physical damage to the casing or the innards.
Most lithium-based batteries have a venting valve which opens when the internal pressure exceeds some threshold value above the ambient pressure. I believe the pressure differential which triggers the vent is somewhere between two or three atmospheres. The purpose of the valve is to allow gases produced by a fire inside the battery to escape, preventing an explosion which would make a bad situation even worse.
The difference between cabin/cargo hold pressure at sea level and FL350 is a little less than one atmosphere. In normal flight, it would be impossible for the pressure differential across the wall of a battery to ever exceed one atmosphere. Even in the event of a sudden decompression, the pressure differential would not exceed one atmosphere, and the venting valve would not open.
There is, however, another factor which needs to be taken into account. The rate of change in the pressure differential may produce unexpected results. A sudden reduction in the ambient pressure in the cargo hold, not equalized by an open venting valve, could cause the battery to swell. Sudden swelling could cause the internal components of the battery to shift relative to one another, possibly leading to physical damage and resulting in a fire.
If this sequence took place on MH370, then decompression would have led to a fire, rather than the other way around. Two events usually assumed to be unrelated would both have taken place.
Unfortunately, I cannot find on the internet any description of the effects of sudden decompression on lithium-based batteries. Does anyone know what happens?