1. Batteries contain sulphuric acid, which can cause considerable harm if it comes into contact with your skin. Always wear the correct personal protective equipment when handling a battery. They can also produce mixtures of hydrogen gas and oxygen which can explode if they come in contact with heat or sparks.2. When removing a battery from a machine, always disconnect the ground cable first and mark the cables as positive and negative so that when a battery is reattached it is done correctly.