In fact, incorrectly charging a battery can cause it to EXPLODE and RELEASE POISONOUS AND/OR CORROSIVE GASES, LIQUIDS, AND/OR SOLIDS.

A battery is an electro-chemical device - and many of the chemicals are pretty nasty!!

As has already been said, there is absolutely no point in just saying "battery charger" - each specific battery type (Lead/Acid, NiCd, NiMH, Li-Ion, etc, etc) has its own specific requirements and therefore needs a specific type of charging circuit; even when the type of battery is known, different circuits will be required depending on the type of duty; eg, fast charge, float charge, deep cycle,...