WHY YOU NEED A CHARGE CONTROLLER
An overcharged battery will boil the sulfuric acid and distilled water mix. The casing of the battery can become hot to the touch, and begin to melt or swell. Flammable hydrogen can build up inside the sealed cells of the battery, causing swelling of the casing under pressure and seepage through small vents. Once the hydrogen is introduced to oxygen, it becomes a sitting time bomb. A small electrical spark can ignite the gas and cause the battery to explode, sending plastic and lead shrapnel flying around, in addition to a caustic sulfuric acid spray.