Look for labels such as “POS,” “P,” or “+” for the positive post and “NEG,” “N,” or “-“ for the negative (grounded) posts on the battery case. Compare the diameters of the battery posts. For most batteries, the positive post is thicker than the negative post. If the battery cables are connected to the posts, note the color of the cables. The cable connected to the positive post should be red, while the cable connected to the negative post should be black. [4] X Research source
Typically if the battery you’re charging is for a boat, you must take the battery out of the boat and charge it on shore. You can charge the battery inside the boat only if you have a charger and other equipment that is specifically meant for doing so. [5] X Research source Using a battery carrier to move the battery from the vehicle to the place where you will connect it to the charger is recommended. This will avoid putting pressure on the battery ends and forcing battery acid out of the vent caps, as might happen if you carry it in your hands.
Do not touch your eyes, nose, or mouth right after cleaning the terminals. Wash your hands immediately. Do not touch any white gunk that may appear on the terminals, as this is congealed sulfuric acid.
Replace the cell caps after filling. Most U. S. batteries, they are equipped with flame arrestors. If your battery does not have flame-arresting caps, put a wet cloth across the top of the caps. If you have a battery that does not need filled with water (known as maintenance free batteries) or if your battery caps are sealed then you should ignore this step and follow the manufacturer’s instructions for charging your battery.
Never place the charger directly above or below the battery. [7] X Research source
If your charger has an adjustable rate of charge you should start at the lowest rate.
If the battery has not been removed from the vehicle, connect the battery charger’s grounding cable to a heavy-gauge metal part of the engine block or chassis. This prevents arcing at the battery terminal and will not run the risk of causing the battery to explode. Clipping the grounding cable directly to the negative battery terminal can be dangerous. If the battery has been removed from the vehicle, you should connect a jumper cable or insulated battery cable at least 24 inches (60 cm) long to the grounded post. Then, connect the battery charger clip for the grounded post to this cable. This allows you to be away from the battery when you complete the circuit in case it explodes. It is also a good idea not to be facing the battery when you connect the charger to the jumper cable.
Use an extension cord only if absolutely necessary. If an extension cord is necessary, it should be a grounded (three pronged) extension cord and be the proper wire size to accommodate the amperage of the charger. An adapter should not be used between the charger and extension cord or the extension cord and the wall.
Some battery chargers have an engine starting feature. If your battery charger has one, you can leave it connected to the battery when you start the vehicle’s engine; if not, you must disconnect the charger before you start the engine. In either case, avoid moving engine parts if you start the engine with the hood raised or cover removed.
