Runaway Batteries
 

Does anyone knows how to stop a battery (NiCad) running away on commercial jets ? Did you ever witness one exploding ? Thank you.

Remove the charging current & the runaway condition stops.

This is usually done by switching off the battery!

Explosion can be quite dramatic if the battery has been charged in a sealed container. During charge, hydrogen gas is released - if there is ignition there is violent reaction. Ni-Cads should always be charged with battery vents clear and in a well ventilated area.
There is a special catalitic converter which turns hydrogen into water for sealed charging.

Thermal runaway is very dangerous. I once saw a cessna tweetybird trainer with half it's nose blown off from a runaway battery.

You should monitor the temp lights of the battery when in use(if equiped), and if a high temp is detected, shut power down from the battery, and if possible disconect the battery. Allow battery to cool. If battery is in a runaway condition, you may try to cool it with a co2 extinguisher, but be cautious, as it may explode if it is too hot.