I've played with batteries for years and only had one explode (but it only takes one). It was actually more of a pop if you ask me. Anyway, it exploded when I removed the charger wires from the battery and had a spark.

To prevent a spark make sure you turn the battery charger to off when you disconnect the wires. Sometimes unplugging the charger from the wall leaves a drain on the battery which will make a spark.

If there is no ignition source it will not explode.