[header] How to tighten a drive belt [title] Disconnect the battery. [step] Before you get started, disconnect the battery to ensure the engine cannot be started while you're working under the hood. As a precaution, always disconnect the battery before putting your hands in the engine bay of your vehicle. 
Use a hand or socket wrench to loosen the nut holding the ground cable on the negative terminal of the battery, then slide it off the terminal post. You will not need to disconnect the positive cable as well.